You prob won't have any lucky having them activate another carrier's phone. My sister tried activating a Sprint phone and they wouldn't do it. Also a Verizon phone would have to be flashed so the radio would recognize the Sprint network instead of the Verizon network.
VM doesn't allow outside phones on their network, the one method that works puts you in violation of cloning laws. Discussion of this gets people getting banned on on most forum. Bottom line, you can't legally use any other phones.