Right now I'm under an AT&T family plan (voice only). I'm thinking of buying a used iphone 3G from ebay, and use my current sim card. Here are my questions: 1) Will AT&T find out I'm using an iphone and force me to add data plan? I don't need one since I have access to wifi everywhere on campus. 2) Do I need to activate & jailbreak & unlock the iphone before using it? Thanks a lot for your help!