Is it possible to move from Verizon to t-mobile? I'm on a family plan with 5 iPhones: 6s, 5S, 5S, 5, and 5. All are either paid in full (the 6s) or are out of contract (beyond 24 months). I mean, according to the verizon website, they are all "available for upgrade". T-mobile says they have to be unlocked. I think they are, right? They also say they need to be GSM compatible. I read different arguments about this, too. Is there any easy way to check if they are GSM compatible? Thank you!