Develop Bugs

[Q] GPE Rom question

I want to preface this first by saying that...
A. I am not a developer
B. I have huge respect for developers, i know it's not easy
C. I am familiar with rooting/flashing/adb/ etc, just not about Rom development
my question....
The HTC One GPE edition is no different from our VZW phone right? Shouldn't the Rom be able to be directly ported over without issue?
Or does the phone being LTE/Verizon cause issues?
Now i know it's not that easy or this clearly would have been done.... I am just wondering why the GPE roms are not directly able to be flashed on our phones.
Also, if i leave Verizon, and go to T-Mo, would i be able to flash a GPE RUU and have the phone work?
Thanks for anyone with any insight. Just curious about getting a true 100% pure GPE rom on my phone....

IIRC our model primarily uses a CDMA radio while the developer edition uses a GSM based radio. If you directly flashed the GPE ROM you would most likely kill your phone's radio.

mooseknuckles said:
I want to preface this first by saying that...
A. I am not a developer
B. I have huge respect for developers, i know it's not easy
C. I am familiar with rooting/flashing/adb/ etc, just not about development itself or Roms
my question....
The HTC One GPE edition is no different from our phone VZW right? Shouldn't the Rom be able to be directly ported over without issue?
Or does the phone being LTE/Verizon cause issues?
Now i know it's not that easy or this clearly would have been done.... I am just wondering why the GPE roms are not directly able to be flashed on our phones.
Also, if i leave Verizon, and go to T-Mo, would i be able to flash a GPE RUU and have the phone work?
Thanks for anyone with any insight. Just curious about getting a true 100% pure GPE rom on my phone....
Click to expand...
Click to collapse
Your second question is primarily the reason. Our phones run on CDMA/LTE technology. the GPE ROMS are based on GSM technology. so even though you probably could flash one of their ROMS, you more than likely would not have any data or not be able to make phone calls or send text. To answer your last question, I believe these phones are carrier unlocked carrier so you could technically pop in a Tmobile SIM and get their 2G or 3G service(with the right APNs with our current ROMS). I see that people are doing this with their ATT/TMobile/Unlocked phones but I havent heard of anyone getting it to work on the CDMA variants(VZW/Sprint). http://www.youtube.com/watch?v=8G8JXdPk-no
Have you tried some of the GPE modded Roms we have for VZW?

mademan420 said:
Your second question is primarily the reason. Our phones run on CDMA/LTE technology. the GPE ROMS are based on GSM technology. so even though you probably could flash one of their ROMS, you more than likely would not have any data or not be able to make phone calls or send text. To answer your last question, I believe these phones are carrier unlocked carrier so you could technically pop in a Tmobile SIM and get their 2G or 3G service(with the right APNs with our current ROMS). I see that people are doing this with their ATT/TMobile/Unlocked phones but I havent heard of anyone getting it to work on the CDMA variants(VZW/Sprint). http://www.youtube.com/watch?v=8G8JXdPk-no
Have you tried some of the GPE modded Roms we have for VZW?
Click to expand...
Click to collapse
I did use Newt's GPE ROM when i had the DNA, and it worked fairly well. I have not tried any yet on the One, since i only got the phone a few weeks ago. It looks like they are customized, and i am looking for pure GPE no mods at all. But i still might give the other GPE rome a try, have you tried them? any feedback? Part of me thinks i might make the leap to the CM KitKat build since it seems relatively stable....

mooseknuckles said:
I did use Newt's GPE ROM when i had the DNA, and it worked fairly well. I have not tried any yet on the One, since i only got the phone a few weeks ago. It looks like they are customized, and i am looking for pure GPE no mods at all. But i still might give the other GPE rome a try, have you tried them? any feedback? Part of me thinks i might make the leap to the CM KitKat build since it seems relatively stable....
Click to expand...
Click to collapse
Im running Santod's tiKtaK ROM as we speak. It's 4.4 as well and its really vanilla. Beats is the only main thing that doesnt work in it but he says he will look into it. http://forum.xda-developers.com/showthread.php?t=2531235

mademan420 said:
Im running Santod's tiKtaK ROM as we speak. It's 4.4 as well and its really vanilla. Beats is the only main thing that doesnt work in it but he says he will look into it. http://forum.xda-developers.com/showthread.php?t=2531235
Click to expand...
Click to collapse
Beats is not a deal breaker for me. I just need good in call audio, data/wifi/signal, tether, and stability. No extra jazz for me.....
I do like how these builds get quick updates so far. makes my little time with verizon left worth while. i am debating jumping to tmo come summer time....

Google Edition

Hey guys,
I was wondering if there's anyway to convert my Verizon HTC One into Google Edition HTC One, with OTA updates and all of that.
I review this guide here: http://htc-one.wonderhowto.com/how-...with-bootloader-recovery-ota-updates-0148068/
But somewhere in the comments someone asked if it could be done for Verizon and the answer is "NO". So here I am asking again on XDA if someone have found a way to do this...

hophamson said:
Hey guys,
I was wondering if there's anyway to convert my Verizon HTC One into Google Edition HTC One, with OTA updates and all of that.
I review this guide here: http://htc-one.wonderhowto.com/how-...with-bootloader-recovery-ota-updates-0148068/
But somewhere in the comments someone asked if it could be done for Verizon and the answer is "NO". So here I am asking again on XDA if someone have found a way to do this...
Click to expand...
Click to collapse
head on over to the original development section. get yourself S-offed so you can flash roms.
install a google play edition rom from the android development section. there are two there I believe.

hophamson said:
Hey guys,
I was wondering if there's anyway to convert my Verizon HTC One into Google Edition HTC One, with OTA updates and all of that.
I review this guide here: http://htc-one.wonderhowto.com/how-...with-bootloader-recovery-ota-updates-0148068/
But somewhere in the comments someone asked if it could be done for Verizon and the answer is "NO". So here I am asking again on XDA if someone have found a way to do this...
Click to expand...
Click to collapse
ddurandSGS3 said:
head on over to the original development section. get yourself S-offed so you can flash roms.
install a google play edition rom from the android development section. there are two there I believe.
Click to expand...
Click to collapse
If I read this correctly, you want to make your Verizon phone a true GPE most likely in order to get the OTA 4.4 update. This is not possible because there is no official CDMA GPE. But as ddurandSGS3 suggested, you can get a custom GPE ROM in order to make your One basically like the GPE. Then you will not be getting any Google OTA Updates, but the Dev's will more then likely be updating their ROM's to 4.4 when they can.

I'm curious on this as well. I'm on AT&T, but my friend is on Verizon. I'm not a fan of custom ROMs, as I like to use original HTC software. That said, I'm thinking there must be a way or tweaking settings on the GPE (and/or Developer Edition) to get them working properly with Verizon. For starters, the following CDMA compatible network types are available in the phone menu (*#*#4636#*#* > Phone Information) for the Dev Edition:
CDMA auto (PRL)
CDMA only
EvDo only
CDMA + LTE/EvDo auto
CDMA/EvDo/GSM/WCDMA/LTE auto
LTE, CDMA
I know there's a little more to it than that when using Verizon, but surely it's a start. The goal is to have an unbranded phone with OTA updates working. With AT&T, it's easy. Why anybody wanting this would stick with Verizon is beyond me. This is why I left them in 2007 back when I was flashing my V3m and V3c RAZR to unbrand it. It was a lot of work, and I became good with it, but I decided that I shouldn't have to go to that much trouble just to make my phone the way it should've been in the first place.
That's my short rant. The root question remains... How to use the GPE (or Dev Edition) software on Verizon when you don't want to use a custom ROM.
While I would love nothing more than to use his HTC One for testing purposes, he isn't able to part with it long enough for me to make any progress or at least get some answers.

EsJayEs said:
I'm curious on this as well. I'm on AT&T, but my friend is on Verizon. I'm not a fan of custom ROMs, as I like to use original HTC software. That said, I'm thinking there must be a way or tweaking settings on the GPE (and/or Developer Edition) to get them working properly with Verizon. For starters, the following CDMA compatible network types are available in the phone menu (*#*#4636#*#* > Phone Information) for the Dev Edition:
CDMA auto (PRL)
CDMA only
EvDo only
CDMA + LTE/EvDo auto
CDMA/EvDo/GSM/WCDMA/LTE auto
LTE, CDMA
I know there's a little more to it than that when using Verizon, but surely it's a start. The goal is to have an unbranded phone with OTA updates working. With AT&T, it's easy. Why anybody wanting this would stick with Verizon is beyond me. This is why I left them in 2007 back when I was flashing my V3m and V3c RAZR to unbrand it. It was a lot of work, and I became good with it, but I decided that I shouldn't have to go to that much trouble just to make my phone the way it should've been in the first place.
That's my short rant. The root question remains... How to use the GPE (or Dev Edition) software on Verizon when you don't want to use a custom ROM.
While I would love nothing more than to use his HTC One for testing purposes, he isn't able to part with it long enough for me to make any progress or at least get some answers.
Click to expand...
Click to collapse
I think it all boils down to Verizon not allowing unknown devices on their network. They claim it is to maintain the integrity of their network, but it seems like a big crock to me. That is why many unlocked phones cannot just pop in a Verizon SIM and work. Seems pretty stupid to me, but that is how it works these days...

But... What about phones that did come from Verizon? The ESN/IMEI/MEID would remain the same, so Verizon will see their phone on the network.

EsJayEs said:
I'm curious on this as well. I'm on AT&T, but my friend is on Verizon. I'm not a fan of custom ROMs, as I like to use original HTC software. That said, I'm thinking there must be a way or tweaking settings on the GPE (and/or Developer Edition) to get them working properly with Verizon.
Click to expand...
Click to collapse
What you're proposing is impossible. It's more than just a setting in the #*#*4636#*#* menu. The device has to actually have CDMA binaries installed to even communicate on Verizon's network in the first place. The GPE builds for the HTC One are specifically for the model sold through the Play Store, which is a GSM device.
Verizon HTC One owners require the help of devs to port the GPE ROM over by inserting and configuring the CDMA binaries so that it works with our special snowflake radio configuration. There are two such ROMs in the dev section right now.

There is no way to do it, but there are some great GPE ROMs you can use. It's not the same as OTAs, but you'll get what you need without waiting too long. The debs here are great and work quickly

[Q] Non-carrier firmware vs carrier firmware

Hello all,
I'm just wondering, do you guys notice or know of any real difference b/t the unlocked/non-carrier firmware that's out there and the carrier-specific firmware from T-Mobile for the M8? Is one considered better than the other?
Please share your thoughts with us!
Thank You,
RockStar2005

RockStar2005 said:
Hello all,
I'm just wondering, do you guys notice or know of any real difference b/t the unlocked/non-carrier firmware that's out there and the carrier-specific firmware from T-Mobile for the M8? Is one considered better than the other?
Please share your thoughts with us!
Thank You,
RockStar2005
Click to expand...
Click to collapse
I know my experience with the M7 (yes i know its an M8 forum but still somewhat relevant) is Yes, the carrier firmware was better.
I had a Stock TMO branded M7. I did the full conversion to make it a GPe unit. It was nice but i had some signal issues. It was better with the TMO radios but ultimately i put it back to stock TMO and for me i got the best results like that.

IAmSixNine said:
I know my experience with the M7 (yes i know its an M8 forum but still somewhat relevant) is Yes, the carrier firmware was better.
I had a Stock TMO branded M7. I did the full conversion to make it a GPe unit. It was nice but i had some signal issues. It was better with the TMO radios but ultimately i put it back to stock TMO and for me i got the best results like that.
Click to expand...
Click to collapse
No I think the M7 experience is definitely still relevant!
Ok, you're the first one so far here to say that. So the radios change based on the firmware? Why is that? I mean, why would the radios be affected by the firmware? Seems to me it'd be better to leave the radios alone and let them remain how they came.
My previous OTA was from T-Mobile, but in order to get updated ViperOne M8, I had to get the firmware for 2.22 and T-Mo wasn't deploying it. They apparently just approved it on the 18th, but as u prob read above, I'm not even sure if they've deployed it, and what it contains. I seem to have as much signal quality as before. I just wish they'd have VoLTE deployed for the M8s. That would be great.
RockStar2005

I have been with T-Mobile less then 2 years. Prior to that i was with sprint over 10 years. I got most of my "radio" experience flashing different radios for the Samsung GS2.
That device was super finikey when it came to radios. I also found at the time that 3 different network vendors set up most of the CDMA network in the USA for Sprint. So for me having a specific radio work well meant that same one might not work so well up north. Samsung was also known to not have very good hardware / antennas (when i say radios i am referring to the firmware for the specific device.) So while my devices hardware stayed the same Samsung was making software tweaks during each revision of software.
But to keep it simple, Yes, different versions of radios can work differently in each device. Thats even with stock radios. Then if you add stuff like a GPe radio to a stock unit, or what i had with my M7 using a GPe ROM with a TMO radio. It always pains me to see people who post about using carrier A phone unlocked with carrier B network. Those people will never get the most out of their hardware network wise because carrier B has worked with the manufacturer to make sure their device is created to be specific to their network. Sure an unlocked will work but not at 100% efficiency. It could be a hardware limitation, could be some software that is baked into the ROM to make it work better, or even as simple as TMO baking in WiFi calling with their network.
I mean look what happened to the Note 3 for TMO. Originally it shipped with LTE not even enabled. The hardware was there then BAM, with an OTA LTE was enabled. Flash forward to the last few months, 2 separate updates for VoLTE. Those are radios updates that are specific to the hardware in the Note 3.
Hopefully someone else can chime in as well. Id hate to think im the only one.

Six,
No you explained that rather well! My cousin has the Note 3 so I know what u said about the last part (on VoLTE) is def true. I wish HTC would hurry the F up and give us M8 ppl VoLTE. Would be nice. And make it available everywhere, not just major cities (it's avail in Chicago, but I live 25-30 min away).
I have a buddy who works for U.S. Cellular corporate, and he said the same thing. Unlocked phones, esp ones sold by one carrier but used on another's network, don't work AS well as when the phone is made for your carrier's network. International phones at least I believe work fine if released OFFICIALLY in the U.S. (i.e., Sony's Xperia Z2, which is ONLY avail that way in the U.S.), because they've been tested on ALL carrier networks/bands, but that's diff than using say a Sprint phone on T-Mobile's network, I believe. (Or using a phone that wasn't approved for all the major U.S. carriers.)
So far you're the only who seems pro-carrier firmware/OTAs, but that's ok. That's why I started this thread, so I can get all sides of the story. But if you read the previous posts, the other posters make a compelling argument that's pro-noncarrier. It sounds like in my situation I'm fine, b/c I'm pretty sure the int't M8 was tested on T-Mo's bands already. The firmware would just go along with that same data, so I don't think I'm having any loss of quality. Now if I carrier-unlocked my phone and tried it on Sprint or Verizon, or even AT&T......... then I would expect a loss of quality at some level.
Thanks,
RockStar2005

Agreed. I see merits in both custom roms, stock roms, GPe Roms and Cyanogen.
Back in the GS2 days i was a big fan of using some of those custom ROMS guys would cook up. It fixed a lot of issues with Android.
But for ME, since 4.2.2 and up, i have been happy with stock ROMs.
In fact i almost always ran custom roms on my older devices and only recently started to leave them stock.
The last thing was when TMO gave me 3 GB free tethering, that was the last thing i might have rooted for.
My note 3 is stock, my M8 is still stock. and my back up M7 is stock (after putting GPe on it for a few weeks and testing stuff out).
I for one use my M8 as my daily phone and my Note 3 as my back up / game device.
For example, today at lunch i had local news streaming on my M8 while my Note 3 was tethered to my M8. On my Note 3 i was playing a few games while i waited for my food then answered a few emails and chatted with a friend on Hangouts.
With TMOs recent 4.4.3 update my M8 seems to run better then before and i feel im getting better battery life out of it.
Cant wait for my Note 3 to get 4.4.3 or 4.4.4. Also really looking forward to Android L on both of the units.
The way i look at it is what are YOUR pros and cons. LOL.

IAmSixNine said:
Agreed. I see merits in both custom roms, stock roms, GPe Roms and Cyanogen.
Back in the GS2 days i was a big fan of using some of those custom ROMS guys would cook up. It fixed a lot of issues with Android.
But for ME, since 4.2.2 and up, i have been happy with stock ROMs.
In fact i almost always ran custom roms on my older devices and only recently started to leave them stock.
The last thing was when TMO gave me 3 GB free tethering, that was the last thing i might have rooted for.
My note 3 is stock, my M8 is still stock. and my back up M7 is stock (after putting GPe on it for a few weeks and testing stuff out).
I for one use my M8 as my daily phone and my Note 3 as my back up / game device.
For example, today at lunch i had local news streaming on my M8 while my Note 3 was tethered to my M8. On my Note 3 i was playing a few games while i waited for my food then answered a few emails and chatted with a friend on Hangouts.
With TMOs recent 4.4.3 update my M8 seems to run better then before and i feel im getting better battery life out of it.
Cant wait for my Note 3 to get 4.4.3 or 4.4.4. Also really looking forward to Android L on both of the units.
The way i look at it is what are YOUR pros and cons. LOL.
Click to expand...
Click to collapse
My "pros and cons" list involves having all pros and NO cons! lol
I think I'll prob just wait for the T-Mo OTAs from now on, but then again, b/c I have ViperOne, I won't know when they get deployed unless I constantly revert back to stock. Ughh! I guess so far I haven't really noticed a difference in signal and call quality since installing a non-carrier firmware, though it's only been like not even 2 weeks yet since I did it.
That's cool though that you're so happy with it. Perhaps your posts are an indication that T-Mobile has gotten better with their overall quality, and so that's something to look forward to for when I do go back to stock (whenever that is lol).
Thank You,
RockStar2005

Most people make a big deal about carrier OTAs. So you really dont need to revert back to check for them. As long as your active on the boards you will know when a device gets an OTA.
I failed to mention that part of why im happy with stock is because devices are now getting to the point where they are so fast that having bloat ware on them doesnt noticeably slow down the devices like they used to. At least i dont notice it. Pluse with 4.2.2 they allow you to "disable" most apps you dont want to use. So thats another plus.
Back in the day i used to root and do the custom ROM for extra battery life, or tethering, or to make the device snappier.
I honestly would have thought that someone else might have chimed in by now and added their 2 cents.

IAmSixNine said:
Most people make a big deal about carrier OTAs. So you really dont need to revert back to check for them. As long as your active on the boards you will know when a device gets an OTA.
I failed to mention that part of why im happy with stock is because devices are now getting to the point where they are so fast that having bloat ware on them doesnt noticeably slow down the devices like they used to. At least i dont notice it. Pluse with 4.2.2 they allow you to "disable" most apps you dont want to use. So thats another plus.
Back in the day i used to root and do the custom ROM for extra battery life, or tethering, or to make the device snappier.
I honestly would have thought that someone else might have chimed in by now and added their 2 cents.
Click to expand...
Click to collapse
Six,
Yeah, that's true. Or I can check on T-Mobile's update site, though there may still be some delay b/c of how they deploy OTAs: http://support.t-mobile.com/docs/DOC-10366
I've noticed that too, and before I got ViperOne and also Titanium Backup, I was disabling several apps too. Though I prefer to just uninstall them.
RockStar2005

Six,
I talked to one of the ppl at Team Venom, and he said he has T-Mobile and recommends just taking T-Mobile's firmware updates for better cell reception. I'll do that from now on. But for now, if anyone is interested, I have here a link to the latest radio image file for the M8 (as of 8/27). Just download and "install flash" in TWRP.
And if you're rooted and want to get rid of the "red splash" screen during boot-up, try flashing the attached mod! :victory:
http://www.mediafire.com/download/beucjivbc4i9y3u/RadioUpdate_2.22.531.5_1.19.213311491.03G.zip
Thank You,
RockStar2005

So... My question now.. I'm one of those buy vzw m8 take over to T-Mobile. I'm running viper 2.3. It runs great. But vzw never updated to newest firmware.so my question I guess is... Can I flash a T-Mobile radio or firmware to my vzw phone? I kinda know the answer, but I'd rather ask. So if I can.. that'll be great!
Sent from my HTC One_M8 using XDA Free mobile app

I know on the M7 that would brick the unit.
The CDMA and GSM units had different hardware and flashing any GSM ROM into a CDMA unit bricked them.
I want to say the same holds for the M8.
Can someone else confirm that for me?

IAmSixNine said:
I know on the M7 that would brick the unit.
The CDMA and GSM units had different hardware and flashing any GSM ROM into a CDMA unit bricked them.
I want to say the same holds for the M8.
Can someone else confirm that for me?
Click to expand...
Click to collapse
Yeah thanks I kinda figured that, but you know it never hurts to ask, especially if it has the potential to maybe work out.
Sent from my HTC One_M8 using XDA Free mobile app
---------- Post added at 08:23 AM ---------- Previous post was at 08:20 AM ----------
Then maybe would it be better for me when Verizon gets the ota for 4.4.3.... I should implement that, and then.... Redo my rom?
Sent from my HTC One_M8 using XDA Free mobile app

[Q] Regarding WiFi Calling...

With the release of the M9, I've been considering trying to find a good condition used M8 for cheap(ish).
I'm no stranger to unlocking and modding a phone, but I'm having a hard time getting a handle on WiFi calling on this one. It seems like it kind of works on some mods but requires certain radio versions be flashed, and a lot of situations are solved by giving up and flashing a T-mo stock OS. Then there's the inclusion of WFC into Android as a stock feature at some unknown point in the future, maybe 4.1 but only on the Nexus 6 at first..?
So for those of you who actually already own the phones and have been playing around with them for awhile now, do you think it's even worth getting an unlocked/non-Tmo M8 if I need to have WiFi calling? Or is it better to just get a T-mo M8 to start with and deal with de-bloating it? And how bad do you think the bloat is in the first place?

Brew78 said:
With the release of the M9, I've been considering trying to find a good condition used M8 for cheap(ish).
I'm no stranger to unlocking and modding a phone, but I'm having a hard time getting a handle on WiFi calling on this one. It seems like it kind of works on some mods but requires certain radio versions be flashed, and a lot of situations are solved by giving up and flashing a T-mo stock OS. Then there's the inclusion of WFC into Android as a stock feature at some unknown point in the future, maybe 4.1 but only on the Nexus 6 at first..?
So for those of you who actually already own the phones and have been playing around with them for awhile now, do you think it's even worth getting an unlocked/non-Tmo M8 if I need to have WiFi calling? Or is it better to just get a T-mo M8 to start with and deal with de-bloating it? And how bad do you think the bloat is in the first place?
Click to expand...
Click to collapse
For t-mobile wifi calling I believe you need to have the phone setup as a t-mobile phone. So if the phone is a non-t-mobile phone, you need to run a t-mobile ROM, which might include flash different firmware and setting other items. From what I know, the ROMS that have the t-mobile wifi calling in them used the t-mobile ROM as a based (but I could be wrong), and those that do not typically are other GSM based ROMS.
Remember that depending on your plan, you could just use google voice over 3g/4g or wifi also.

Kind of figured it was something like that, thanks. In the end, I actually wound up with a Moto X since they had that package deal with the headphones last week and I was in the market for a new set anyway. Guess I gotta do without Wi-Fi calling for now.

This user was able to get it to work, so you might try flashing this: http://forum.xda-developers.com/tmobile-htc-one-m8/general/t-mobile-wifi-calling-t3058708

HTC One M9 Variants to avoid buying (rooting, bootloader unlock, s off)?

My LG G4 is dead and i need a good substitute ASAP on a tight budget ($200-$250 max). This pretty much limits me to 2015 era phones. Not getting another LG, Samsungs are too expensive and S6 has no microSD slot anyway. Narrowed it down to either an HTC One M9 and Moto X Force. Moto's limited development as well as an alarming number of nightmarish defective OLED displays has scared me off of it (shame as I love OLEDs).
So i'm about settled on an HTC One M9. I did my best to research any deal breaking hardware defects, any problems seem far less severe or common compared to G4 or Moto. Assuming I haven't missed anything...
So that said my question now turns to the software side- are there any carriers/variants of the M9 I should try to avoid buying? As the title says, I wish to unlock the bootloader, root, and eventually install custom roms etc. I'm prepared to pay for Sunshine if necessary provided all M9 variants are supported. I've done my best to read through as many threads and pages as I could before asking this. It SEEMS like i'd be safe buying pretty much any M9 and still be able to unlock bootloader, root and s off. Even Verizon models if i'm not mistaken? Am I correct in this assumption? I wanted to ask just to ensure I didn't miss any important caveats before buying.
I messed up buying an LG, many suffer from a motherboard defect causing unfixable bootlooping and mine finally succumbed the other day. Mine was also a region that didn't allow bootloader unlocking. I could root with some effort if I didn't mind being stuck forever on lollipop, but no custom roms and other annoying limitations.
I don't wish to repeat the same mistakes if I can avoid it, so any information regarding my query would be greatly appreciated. Any other advice or things to look out for regarding the M9 would be helpful too. Thanks very much in advance.
By the way, the version i'm looking at buying is listed as an AT&T model. From what I have seen, this variant seems to be pretty much perfect for doing all I want. But I still wanted to ask this in case I either get a different variant, or if the seller is listing the wrong version of the product. If all M9s are basically equal at this point, then I don't need to worry which kind I get.

Try to buy a worldwide edition. It's the sim unlocked from factory with region 401 ie x.xx.401.xx firmware version.
M9 is a solid phone. The camera isn't the greatest but it does take good shots. It can get a bit hot if charging and playing games at the same time and it is more than capable of draining the battery in an hour or two if you use resource intensive games or apps. The sound is very clear and boomsound is a major player in the satisfaction this phone gives, making the speakers significantly bassier than other devices on the market. The speakers 'can' be a little quiet at full but they ALWAYS stay crystal clear with no distortion at all.
You MUST get a protector case for this device as the front of the actual phone can crack if you apply pressure, by the front camera lens is cracked on mine. Tech21 make a good sturdy case for this device but it is a tad expensive at £30 GBP.
I Don't recommend using custom roms with this device as not only is the risk of a brick significantly higher it is also going to result in a slightly slower phone than stock rooted.
The different variants of this device are essentially the same but carrier locked versions can be a prick to find software to fix stuff.
In all you've made the right choice of phone if you plan on keeping it stock but the wrong one if you plan on modding it.
Beamed in by telepathy.

Sorry, but I have to disagree with some points of the post above this one.
If you live in the US then choosing either the unlocked/dev variant or the version of your carrier is the best choice. SKU 401 is optimized for the EU (in regard to supported frequencies and some GPS configurations). And it's important that you choose the correct hardware version for your carrier's technology (Verizon & Sprint: CDMA - all other variants: GSM). The firmware of CDMA devices and GSM devices isn't interchangeable. You can't even flash Sprint firmware on a Verizon device (or vice versa) without damaging it. However, you can change from one GSM firmware to a different one if you want to (S-OFF required).
Just for having it mentioned (I know that you don't need this information but who knows who else is going to read this): The Verizon version's bootloader cannot get unlocked via HTCdev (unlike the bootloader of all other versions). You need S-OFF for unlocking the bootloader of that version. Since sunshine needs root on the latest firmware version the only way to unlock the Verizon variant on the latest firmware is an xtc clip/java card. (This may change with a future update of sunshine.) Or you try to get a pre-Nougat Verizon M9 and use the temp-root of the sunshine app.
In addition, HTC provides RUUs for its US devices. Therefore, getting back to stock is easier with one of them than with all other non-US variants.
And in regard to custom roms: They don't hardbrick your device. The worst thing that can happen is a soft-brick/bootloop and that will only happen if you try to flash a custom rom whose base is newer than your phone's firmware (and some nougat roms are even compatible with the marshmallow firmware so this happens quite rarely in the recent time).
Aside from that, my phone is as fast while I use Viper 6.1 as it has been while I was playing around with the stock rom. If there really is a difference then you need laboratory equipment for being able to detect it. And I'm pretty sure that you get the same performance on other (sense-based) custom roms, as well.
The only thing that you need to be aware of is that there are more and more reports of dying memory chips. These nand deaths happen on stock phones and on modified phones. As far as I read, no one has been able to repair such a dead device except for HTC itself. I don't know what's the cause of the problem since I know enough people whose M9's are still working fine without any issues.
Sent from my HTC One M9 using XDA Labs

Thanks for the reply from both of you. I'm surprised and happy a mod actually replied too!
My LG was locked out from installing custom roms and such, but I have experience installing some on a first gen Galaxy S (currently using it as backup in fact). I'm sure things have changed somewhat, but I am aware of the potential risks in flashing custom roms. I've bootlooped and soft bricked my device doing so more than once. I'm not a programmer, but I was able to fix them all with patience, research and the right tools/software. I assume there are also methods to deal with soft bricks and bootloops on HTC One M9 if you consider it less of a threat than a hardware brick (which my LG G4 got even without flashing anything). I appreciate the warning and advice either way.
I'm not concerned with the carrier compatibility that much. I don't have service with anyone at the moment and can use whatever. Seller says the device is a GSM unlocked AT&T device, if accurate then i'm perfectly content with using GSM networks. Listing says "new AT&T carrier overstock item", which I hope means the device is okay. It's being advertised as running 5.0 Lollipop, which I assume means the stock rom it came with when first released and also hope is an okay starting point for doing whatever rooting and customization I want.
I hope the NAND issue doesn't crop up on the one I get though, that doesn't sound good. HTC attracted me because i've seen fewer people complaining about widespread hardware defects compared to many other phones. It's difficult to find phones that are a good value, are reasonably free of serious problems and include features I deem important (microSD card support for instance, and having reasonably fast processors). My options are limited.
I'm not sure if i'll need s off. I'm new to that term and don't know much about it besides it being some sort of HTC security. Not sure what doors would open up by having s off, still researching. Assuming the model I buy is accurately listed as AT&T, it sounds like I should be able to unlock the bootloader, root, flash TWRP and even get custom roms without having s off. Am I correct? Not even sure if it's required to flash kernels such as ElementalX.

That can happen if you post in the forum of a device that's owned by a mod. Don't forget that we're normal members, as well, if we don't moderate.
If you face a soft-brick you only need to keep both volume buttons and the power button pressed until the phone reboots to its bootloader. From there on you can boot to TWRP and only need to flash a working rom or to restore a backup of a working (stock) rom and the problem should be fixed. Hard-bricks only happen if you flash a CDMA firmware on a GSM device (or vice versa) or a Sprint firmware on a Verizon device (or vice versa). The phone will still be booting but from what I observed here on xda your SIM card won't be detected, anymore, even if you re-flash your phone's original firmware. Aside from that you can "kill" this phone if you're impatient while it's installing an update and power it down during the process (there was a time when that happened quite often). Therefore, I suggest you to just let it do it's thing after you started the update process. Depending on which update you want to install it might take up to approximately half an hour and the phone might reboot (and therefore vibrate) several times.
Correct, for flashing custom recoveries/roms/kernels you don't need S-OFF on this phone (as long as it's not the Verizon variant). Take a look at the further reading section of the ReadMe thread. There's an article linked that explains S-OFF. And Sneakyghost's firmware thread in the development section should contain an explanation, as well. If I remember correctly it should be located in the 5th post. Be aware that you don't need to (re-)lock this phones bootloader like you needed to do on older HTC devices if you want to flash a RUU with S-ON as long as you use the SD card method. That's the recommended method, btw.
I personally don't use a custom kernel. They had a huge impact on my last device (the HTC One S - released in 2012) but HTC seems to be learning at least from some of its "mistakes" since the battery optimizations are much better on the M9. Therefore, I haven't been using a custom kernel since one of the early versions of ElementalX. On the other hand, that means that I can't tell you whether the current version got optimized that much that it actually has an impact, again.
In regard to the nand issue: Don't forget that 95% of the posts here get made by people who face problems with their phones whereas most people don't post if everything is working fine. That might cause that an issue seems to be more common than it actually is. And as said in my last post, I haven't seen such a dead nand in real life, yet, and I know a lot of people who own this phone.
And last but not least a little tip: Find out your phone's firmware as soon as you get it. If it's a pre-4.x version (everything before android n) then try to find the latest 3.x RUU for your SKU*. If you install that one you will save some time that would otherwise be needed for installing a huge amount of OTA updates. (A RUU only needs around 5 minutes if you use the SD card method.) You can't directly install a 4.x RUU since HTC changed the encryption keys between firmware 3.x and 4.x. Therefore, you need to install the 4.x update via the software update function of the phone since OTAs aren't encrypted. More information, some useful files and instructions can be found in the ReadMe thread. (It's a big wall-of-text but reading and understanding it is worth the time that you need for doing so.)
Edit: * = Here's a download link for the latest 3.x AT&T M9 RUU (directly from HTC's server). However, now that I think about it I actually can't tell you whether the AT&T variant already received android n...
Sent from my HTC One M9 using XDA Labs