Yes, it`s possible. Your previous carrier might give you information on how to unlock phones purchased through them, so you might want to try asking them. There may be a fee associated with doing this. Or the phone's manufacturer might be able to give you some information about unlocking it.
Even if the phone is unlocked, it might not work on Virgin network. So first, just email your phone's IMEI number to their customer service, so they can look it up in their systems to see if it's compatible.