I was wondering if i purchased a used verizon iPhone 4 or 4s, would i be able to use it on the Sprint network since they are both CDMA? I have a friend who is selling his old iPhone 4 on Verizon and i would like to use it on Sprint since my upgrade is next year and i don't want to shell out a bunch of cash for one. Would it work? If it won't, why not? Thanks!