im going to buy an used iphone. i talked to him on the phone and he sounds friendly enough. according to him, it's only 3 months old, 8 gb, and NOT unlocked or jailbroken. im supposed to meet him tomorrow to pick it up. now, i need advice on what are the things to check for on a used iphone? i personally use tmobile, so i definitely can't use my tmobile sim card on it. i could do the unlocking process myself when i get home, but it would be too late by that time, because i want to make sure it works perfectly fine first before i actually pay him. what would you recommend me to do to 'check' the phone?