A:AnswerI was able to with Verizon. I am pretty sure you should be able to do the same with virgin mobile. If not you could keep the same number and switch to prepaid from Verizon or at&t at a reasonable rate.
A:AnswerAs I understand, the us unlocked version will work with any us carrier. I assume that means it will work in other countries as it has numerous GSM and CDMA bands
2. It will probably cost you to transfer if you signed a contract and got your phone on the payment plan. Otherwise if you bought the phone outright probably not. You will have to confirm with the carrier. ok
3 you need to ask the carrier but my guess is no.