Can you switch a Sprint iphone to a prepaid plan?

My sister has an iphone and wants to give it to me because she is getting an iphone 5.Is there anyway I can use the phone with a prepaid plan and not a contract? Whether it would mean switching carriers or anything is there anyway to use the the iphone prepaid instead of being tied down to a contract?

Sprint has a prepaid plan, call and ask them.

How can i switch my existing iphones to a prepaid plan like straight talk