Curious how this works. Say I decide I want to sell my on-contract, locked 4S to upgrade to an iPhone 5, for which I'm eligible for an early upgrade. 1) What do I need to do to the phone itself to sell it? Do I need to call AT&T and have them do something to it? Do I need to take the SIM out and sell it without it? 2) How do I go about getting the new phone all set up without messing with my contract and keeping my phone number, etc.? I realize I'd have to sign a new two year agreement upon upgrading the phone, that's fine...but I don't want anything in my contract to change in terms of my services or prices. Thanks, just not sure how the actual logistics work of selling a phone in the middle of a contract and what's all involved in preparing the phone for sale.