[Sprint HTC One (M7)] DueceBigelow:
Not to necro this post, but I spent a CONSIDERABLE amount of time this last week going through post after post trying to find a *verified* answer to this question (and others) with no luck -lots of trial and error using various posts for information. The biggest obstacle I encountered is that most the information is geared toward the "GSM" varieties, whereas I have a Sprint HTC One; also requires reading "between the lines" because a lot of the info implies, infers or makes base assumptions, etc.

1.- Unlock bootloader (I did it with the htc dev account).

Easy, step-by-step tutorial by HTC. What this does is allow you to install a custom recovery ROM like ClockworkMod or TeamWinRecoveryProject TWRP

2.- Install custom recovery (I used TWRP).

I too used TWRP, In all honesty, I have absolutely NO idea how I installed it on this hardware. I remember the process of installing on an old Optimus S, but this installation was nothing like that experience. That said, if I can get it done and have no idea how it got done, rest assured you can too

3.- Install SuperSU (Be sure to have the latest version, it won't work otherwise).

One of those things that is not made terribly clear, install through Google Play, reboot into TWRP, it will detect the SuperSU and ask if you want to install it.

4.- Flash the custom ROM "Stock with goodies" (It is referenced in the first posts of this thread).

This is the hard part, because most of the info online is outdated or does not reflect current software releases and/or differences in hardware (AT&T vs Sprint). For instance my Sprint HTC One was Hboot1.57, Android 4.4.2, and Sense 6.0. I got CyanogenMod10 to work, however revone, rumrunner and firewater failed but all available info only talked about hboot 1.56 and sense 5.0. So I spent a lot of time trying to understand what was failing. At any rate, I finally stumbled on a suggestion on something completely unrelated to

try ViperOne_6.2.0 ROM with ElementalX-Sprint-m7-13.1 Kernel to turn S-OFF

. TWRP allows you to select multiple zip files to install in sequence, which I did, but ElementalX process may or may not have installed after ViperOne finished... I don't even know how to check if it is installed, but I pushed forward since the phone was booting and I could make calls again

5.- Flash the file provided in the first post of this thread.

Instructions like this is too ambiguous because what it doesn't tell you is that this step WILL FAIL if certain software requirements are not met!

Run Firewater at this time; this turn

5.a. adding this line, AFTER firewater is done, you will see in the HBOOT that S-OFF is displayed. Now you can boot to recovery (TWRP), goto "Install" and select HtcOMADM_SPCS.zip obviously requires you to download this file first. In all honesty, I have no idea what the heck this does or if it is needed since firewater completed..

6.- Unlock SIM via terminal emulator (The steps for this are also referenced in the first post).

Download and install "Sprint HTC One SIM Unlock Helper". When you first open, it will throw errors "OS Check Fail" and "needs Sense Rom", just hit the back key to get to "instructions" page. Just check that "Device is green and verified", Root is green and available, sense Rom is green and Yes"; Tap on the "start" button and SU will ask what to do with the app, just select always allow. App will take a minute or so to think, you'll get a new menu, black with white font, scroll all the way down to sim lock. Tap that, wait ~1 minutes you'll eventually just get a log when it is all done and a success message.

REFERENCES:

Complete Guide to SimUnlock HTC One

A domestic GSM has not yet been tried in my phone, I am travelling right now and have not found a phone shop nearby yet. Plan on updating my findings