I bought a blue one a few days ago, love it, but had trouble getting S-Off. I bought it to use on T-Mobile. I submitted an unlock request to AT&T through their website and am waiting on a reply. If that fails I'll just buy an unlock code. I wish I would have found this thread sooner.
hboot 1.55
android ver 4.3
software ver 3.17.502.3
radio: 4T.20.3218.13
Unlocked bootloader with htcdev.com no problem. Flashed custom recovery with twrp 2.8.74.0-m7 and root with UPDATE-SuperSU-v2.45.
I could not for the life of me get revone or rumrunner to work, revone -P would fail (even as su), rumrunner would say cleaning skunky rum and have a progress bar where it would request su (granted it) and fail. I tried firewater and it wouldn't run after being pushed to the device. After that I used SunShine ($25) and that was painless and finally got S-Off.
I changed the CID to T-MOB010, I also used MID_Change_1.01 to set MID to PN0713000 (under custom recovery). I was able to flash TMOUS_3.24.531.3 Zip, bringing it to factory recovery, and it did a few OTAs being around 600MB each bringing it to TMOUS_6.10.531.10. For fun I tried to install TMOUS_6.10.531.10 Exe, and it wouldn't continue unless the CID was 11111111.
To switch back to AT&T, I set CID CWS__001 and MID PN0712000 (under custom recovery), flash Cingular_US_3.17.502.3 Zip and I can then flash Cingular_US_3.17.502.3 Exe but not Cingular_US_4.18.502.7 Exe. I can't seem to get any OTA with 3.17.502.3 but I don't have a valid AT&T sim card. I'm pretty new to this stuff and I'll probably just stick to the GPE 5.0.1 Zip (works great).