I'm looking to buy an iphone 4 from a craigslist user. This guy is the original owner with box and receipt and is willing to meet at the At&T store. I am looking to use on Tmobile. To do this, can we just meet up at a local At&t store and get it unlocked and working with my Tmobile SIM card right away? Or is it a process that takes a long time? I don't want to buy this phone and then have to rely on him to verify or confirm emails and stuff and be left with a phone that I can't use. For anyone who has experience unlocking their iphone, I'd love to hear advice. I don't have At&t nor an iphone so I'm kind of out of the loop. I could also ask him to do it over the phone or live chat if that's faster but can't imagine it being faster than in-store. Any help appreciated.