Here's the scenario My friend and I have an iPhone 4. He is eligible for an upgrade, I'm not. He is willing to upgrade his phone and sell me the 4S. He wants to keep his phone as is. If ATT activates the 4S, can he simply put his sim back on his 4 and I put my sim on the 4S? Do I need to do anything with my account (tell ATT I now have a 4S) Does he need to tell ATT, he has sold the 4S. Oh, and like this to be done without losing my unlimited data. Thanks!