The story:

I got this iPhone 4 which is tied to Sprint as partial payment from some people who owe me money. They are now hooked on drugs and falling out of society/not paying any bills. This being said the phone is still connected to their line but they aren't paying their bill. It has a clean ESN and isn't reported as stolen but the people also won't call in and cancel because all of their phones have been shut off / they owe me money so why would they talk to me, ect.

I can't sell this phone because it's tied to someone else's line already, even though it does have a clean ESN. Is there any work around for this?