Add one more to the pile...
I also recently began having this problem, but my device previously worked fine.
I have tried Restoring to Factory V21Y with Mar 11 Baseband
Flasing a GB Based ROM & Stock Kernel
Flashing CM9
Flashing CM10
Entering *#*#INFO#*#* Phone Info and modifying frequency band (No Go).
At one point I was able to read the Phone # from the SIM card, but couldn't get a lock on Netowkr. I can visually detect T-Mobile and ATT in Mobile Networks.
I have tried this with 4G Enabled SIM Cards and older T-Mobile SIM Cards.
I have tried Simple Mobile, Straight Talk, & ATT SIM Cards.
I have tried using None APN's, the TMo/Simple Default APN's, and Modified APN's for Straight Talk & Family Talk.
No avail.
Any ideas?