Unlocking Sprint Phone (eBay)

I bought a sprint iPhone 4s off of eBay. I contacted sprint but they refuse to unlock the phone because I don't have the original phone number password or any other account information. I informed them I purchased it off eBay but they don't care.

Is there any other way to unlock this phone? I've searched google for ways to unlock the phone and the main way is to contact sprint (which I've tried) or attempting to download an unlocker app which I'm thinking is probably a virus or something fishy as you have to complete "offers" in order to be eligible to download the app...

any suggestions?