Can I use a sprint contract iphone 4 with virgin mobile?

I have the chance to get a iphone 4 that is currently used on a sprint contract. Can I use it on my current virgin mobile no-contract plan? Do I have to jailbreak it? Unlock it?

Unlocking and jailbreaking will not get a Sprint phone onto Virgin Mobile, as Virgin Mobile, like all CDMA carriers, needs to have the ESN of the phone to be activated in their "allowed ESN" list, and Virgin Mobile does not add outside phone's ESNs to that list.