I have been running 4.1 jailbreak on my locked att iphone 4 for about a year and a half and decided it was time to upgrade. I have 2.10.04 baseband and wanted to keep it there for the 5.1.1 update, I used what ever program where it makes a custom firmware off of the 5.1.1 update and your iphones base band to preserve the baseband during the update/restore. I think I chose to unlock it using the firmware which I'm not sure if that has anything to do with the problem or not. So I finally got it updated and installed with cydia and all after It finished restoring/updating to 5.1.1, I noticed I had no service and in itunes it shows no phone number in the phone info when it normally did. I installed the latest version of redSn0w and it still wasn't working. I then installed the ultrasn0w fix for 5.1.1 and ultrasn0w but still with no luck. The baseband is still on 2.10.04 so I have no idea what is going on, and I'm still using my current cell service which is att and the sim is in there too.