FWIW, this method worked for me. I had followed the other instructions of finding my code in "bml3", but it didn't unlock my phone (even after restarting it). This method worked as advertised.
For those of you who are a little mystified what these instructions mean or are unsure of how to do this safely, here are some more clues (there are plenty of posts/threads explaining these steps in detail in this forum):
1. Root your phone
2. Get "Android Commander" (a PC application that lets you painlessly move files between your phone and your PC) [[if you are an expert, you don't really need this -- or my clues
]]
3. Copy "/efs/root/afs/settings/nv_data.bin" to your PC. Now, for safety, make another copy of it on your PC called "nv_data.bin-ORIG" or whatever.
4. Get a hex editor. The 010 Editor mentioned in various posts is a popular choice.
5. Edit your PC copy of "nv_data.bin" with your hex editor. Make the change mentioned in nmil's post, save, and exit.
6. Back to Android Commander. Copy your modified PC copy of "nv_data.bin" back to the original location on your phone. You will be overlaying the original copy of the file on your phone.
This is the most sensitive step, so don't mess it up.
7. Restart your phone with a SIM card that is not from T-Mobile. You should be all clear now (no unlock prompt).
Sorry if I belabored the point above, but there are lots of posts around from people who are not very experienced with such things. ("I followed your procedure exactly, and now my garage door won't open.")