Can I use sprint iphone for with the contract up as a sprint prepaid?

My IPhone 4 that I have with sprint is currently up to renewing my contract but instead of getting locked into a 2year.contract can I use the same phone as a prepaid sprint phone. I wasn't sure because I had heard no, that you had to buy the iPhone for a prepaid plan but I have also heard since its the same carrier I should have no problems using it as a prepaid phone.

I'm pretty sure you can't - to use prepaid on Sprint you need a special prepaid-only Sprint phone. This is true for most carriers with prepay, because part of the way they make money off you if you're prepaid is because you're buying the phone - money they won't get if you already have the phone.

But you can always ask Sprint to know for sure.

After your contract ends you can keep using your same phone.

This will be month to month and you can cancel anytime.