Bought a iphone 2G, seller claimed its unlock and jailbroken. When i pop in Tmobile or AT&T sim card in, it get No Service on either card. It work on 911 emergency call. This phone has firmware 3.1.2 and it has cydia icon in, so i assume it has unlocked. I've ask my coworker, he ask me to downgrade firmware, 3.1.2 FW for 3G or 3Gs phone only. My friend said, 3.1.2 FW automatically locked up again since it upgraded. I never unlocked or jailbroken an iPhone. Don't know how to check. Any suggest??