I have an iPhone 3GS running iOS 5.0.1. w/ a 06.15.00 baseband. It's an AT&T iPhone but I'm trying to get it on T-Mobile. The only problem is that I've install Cydia and ultrasn0w but the iPhone fails to pick up any cellular signal with a T-Mobile OR an AT&T sim card installed. It just reads "no service." Is there any proper step by step directions I can follow or am I doing something wrong here? Or have I totally just bricked this iPhone?