Ok. So I am getting geared up for 3G and I want to sell off my 4Gig Iphone. The phone itself is NOT unlocked. What I want to know, is how do I do this wthout giving away my at&t account? Do I take the sim card out? If I take the sim card out, Which SIM card do i put in the phone? P.s. I am on a go-phone plan as I thought that 3g would come out this year and I didnt want to get tied into a contract if its not exclusively AT&T. Help would be appreciated.