Sprint runs a CDMA network. I don't believe Apple sells unlocked CDMA iPhones, only GSM. Maybe that will change when the next model supposedly combines GSM and CDMA antennas in a single model.
Maybe I'm missing something, but why bye an unlocked phone? You pay more up front and the same monthly fee for network access. Is it just the contract you don't want to enter?
The price of the phone is the same whether you pay upfront or through an increased monthly fee, but with the unlocked phone I can pop in a local sim-card if I travel, and I can change my provider whenever I want.
The only benefit for the locked ones are that you get to buy it on what is essentially cheap credit, but it's not like you save any significant amount of money on that.
