Currently Being ModeratedDec 3, 2012 2:14 PM (in response to ZyqL)
Sprint should be able to unlock the GSM portion of the iPhone 4S so you can use it with non-US GSM carriers, but unless Sprint's policies have changed, you cannot use a Sprint iPhone with any other US-based carrier.
Currently Being ModeratedDec 3, 2012 2:49 PM (in response to ZyqL)
Sprint and Virgin Mobile in the US are both CDMA carriers. You can not use a Sprint phone on any other US carrier. You can not us a Virgin Mobile iPhone on any other US carrier.
If you want to use Virgin Mobile, you will have to puchase a phone intended to be used on their network.