[omowasu]

The answer is no but not because of locked down serial numbers. The iPhone 3 was sold by Verizon and ATT. Apple built the handsets to access ATT GSM frequencies and Verizon CDMA frequencies. Since Sprint CDMA resides in a different band than Verizon CDMA, the Verizon phone will not run on the Sprint network (and vice versa), and ATT will not run on either! Someday this will change, probably with the evolution of VoLTE...