Pretty much what the title asks. Let me set this up. I have a 3G, and I'm not eligible for the discounted upgrade, so I would have to pay full price to upgrade me phone. However, I have a co-worker that's interested in an iPhone, and I've offered to give him my phone for free, and buy his new 3GS when he signs up, as long as we can swap the sim cards and the phones will work just phone. He doesn't care what model of phone it is, he just wants an iPhone, and when I offered to just give it to him for free, he was all down for that. So will the swapping of sim cards work? What if one of us needs to take our phone in to have it worked on? Will there be issues with AT&T and/or Apple?