Can I use an at&t iPhone 4S on the Sprint network?

Would it have to be unlocked? From what I hear the iPhone 4S has both CDMA and GSM capabilities built in.

Since its an AT&T GSM phone it could work with Sprint but it would have to be unlocked to work with Sprint a CDMA network. Also you would have to cancel your contract with AT&T.

Yes it should be unlocked, you can't use it on sprint network anyway
Otherwise your cell phone plan from sprint should be no contract cell phone plan