I sold and shipped my iPhone 3G and the buyer is saying that it is not unlocked. It is giving him an "Invalid SIM" message. He's using T-Mobile. It was 3.0, and I jailbroke and unlocked it (using ultrasn0w) myself. There was no SIM card inserted when I did it, but I was under the impression that it was fine: http://forums.macrumors.com/showthread.php?t=742572&highlight=unlock+no+sim+card Before I shipped it out I informed the buyer that I didn't have a T-Mobile SIM card and that he may have to power on/off or reboot it himself, which I have already instructed him to do. I can walk him through the actual unlocking steps and do it again, but is there anything else that he should be doing? Should he call T-Mobile and get the IMEI number switched over? From what I have looked up and been reading, it seems like you just plug in the SIM card and it should work. Can you even, in essence, "reinstall" an unlock?