Wow... it took you two whole days to come on here and tell us how bad the iPhone is. You're slacking.
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Pick up a CL iphone 4s (I talked to a guy about a NIB 16gb yesterday, $350 was his bottom dollar) and get on the T-mobile Sim-only deal after your contract expires. In the meantime, use the new phone on your existing contract.
The Virgin deal will be great if you don't mind paying full price for the phone. Remember that ATT is GSM and Virgin/Boost are CDMA (Sprint network).
There are tons of iPhone 4 and 4S's on CL right now, many NIB, all under $450 for 4S, $250 for 4. You can then sell your 3GS for $150 to recoup some of the cost. Best bet is to ride-out your current plan rather than paying early-termination fee. Also, double check that fee, ATT currently charges $175 early term, with $5/mont reduction for every month of the contract you've completed.