Every Sprint HTC One can be unlocked, you just need a little patience and some basic knowledge. The unlock is PERMANENT, so you won't loose it if you flash another ROM, or even a ruu. The unlock works only on SENSE ROMs, so you can't unlock it on CM, AOSP or GPE ROMs. Even after you have unlocked you won't have network in non-sense ROMs.
Make sure your carrier frequencies are supported by the phone. Here you can find the HTC One's frequencies for Sprint.
Using US carriers will be a bit tricky, cause the frequencies the phone uses do not cover all the regions. You may loose network coverage often and may have problem with the roaming guards. Some users reported that the newest radios block domestic roaming, so you can try directly solution 3 which will downgrade your radio also, or downgrade it manually by flashing THIS radio in recovery. I also suggest you try BadBoyz ROM which has forced roaming.
The unlock works great outside the US though.
Before the release of 4.3 ROMs the process was very easy. If you still are on a SENSE 4.1.2 ROM with root access than all you have to do is follow this guide http://forum.xda-developers.com/show....php?t=2386703 or use the "Sprint HTC One SIM Unlock Helper" from Play Store
Now with the release of 4.3 Sprint made it more difficult. (Note even on the 4.4.2 base nothing has changed, the process is the same) The unlock uses a file called HtcOMADM_SPCS which was modified in 4.3, so the unlock no longer works.
There are 3 possible solutions to this problem.
1. Use the modified HtcOMADM_SPCS made by @chas123 http://forum.xda-developers.com/show....php?t=2534208 You have to flash this in recovery and than the process is the same as with the 4.1.2 ROM
2. Use a file manager to replace the HtcOMADM_SPCS in /system/app with THIS.Than the process is the same as with the 4.1.2 ROM. After unlocking you'll get vDM client crashes. It's not a problem, cause afterwards you can flash any other ROM and you'll remain unlocked.
3. This is the longest way. Do this only if the previous methods fail.
a)If you are already S-OFF than:
-extract zip to a folder on your pc
-boot into bootloader (various ways)
-using fastboot, type this cmd: fastboot oem lock this will relock the bootloader
-from pc, run setup.exe from the extracted folder. it will run the RUU utility & flash back to stock
Now you have to unlock your bootloader, install a custom recovery and root. There are tons of guides for that. You can use THIS
b)If you are S-ON.
You can get S-OFF pretty easily on hboot 1.55 with rumrunner. Instructions HERE
The latest version of rumrunner HERE
If you are on hboot 1.56 or newer you can get s-off with Firewater http://firewater-soff.com/instructions/
After gaining S-OFF the process is the same as explained in a)
After you have successfully downgraded your ROM and radio, gained root you can go ahead and use the unlock. http://forum.xda-developers.com/show....php?t=2386703
How do you check if the unlock was successful?
Pretty simple just insert a SIM card and if you don't get the "SIMLock enabled" message than the unlock is complete.
You may still have no bars and be unable to make calls though. Make sure you change the settings in mobile data, network mode to GSM/UMTS. If still no luck than probably the phone doesn't cover your carrier's frequencies.
If you have signal, but can't use the internet make sure the APN settings match your carrier.
@thatotherguy.. for the unlock thread
@-viperboy- for the Sprint HTC One SIM Unlock Helper
@O.M.J for the ruu
@chas123 for the hacked file which makes unlock possible
If you find this guide useful you can press the "Thanks" button or buy me a coffee