I'm going to eventually upgrade to the new iPhone from the old 3GS (while keeping my old plan with unlimited data). What do people do with their old phones? AT&T has been pushing me to trade it in. Should I? Does the phone work without the SIM card? I've seen people on these boards say that I should ask AT&T to unlock the old phone and sell it online. Is that possible? If so, how do I ask them to unlock it and what does that do? Thanks all.