Hmm, it's possible that one of Sprint's MVNOs might activate a Sprint phone, since they are actually reselling Sprint airtime under their own name. Virgin is the biggest MVNO of Sprint, but I'd have to do some research to come up with more (they're out there!).

That's not a definite 'yes' mind you, because it's up to the reseller if they will activate a used phone or they might want you to buy/own a specific model. You might be able to find some Sprint MVNO prepaid companies just by searching google, that's how I do it.

EDIT: Also, nobody will activate it period if there is an unpaid balance on the account.

Can I use my Sprint pcs phone as a pre-paid?