Sprint iphone bought off craigslist still active on other account?

I bought a Sprint iPhone 4 off of Craigslist andwhen I took it up to Sprint I found out it was active on the guy who sold it to me, his account. He still owes money for his contract. They told me the only way it would work was for him to pay it off. Is this true? Could I get it jail broken and it work on my Sprint account?

Jailbreaking won't help because that won't erase or change the phone's network ID and it won't unlock the phone. Also since it's a Sprint iPhone 4 (not 4s or 5) it is 100% CDMA (no SIM card) and can't be unlocked to work on any other carrier.

But… You might be able to "flash" it (which is a different kind of reprogramming) so that it will work on some other CDMA carrier besides Sprint, for instance Cricket. If you Google for "flash sprint iphone 4 to cricket" you will see some info. You could also ask at a local Cricket store or any other prepay carrier that doesn't use SIM cards. Good luck!

P.S. If you are big and scary, or you have a big and scary friend, maybe the best thing to do would be to visit the guy you bought the phone from and suggest that he give you a refund.