My wife's phone is unlocked we switched carriers I put a new sim in the phone and restarted it the phone worked fine. Next morning it won't let her make or receive calls it says not registered on a network. She can text but no calls. So I try sticking a metro SIM card in and it does the same thing. My first thought was Verizon didn't unlock the phone correctly. So I bought her a new factory unlocked one and it does the same thing!!! Please help I've tried everything I can get it to work for a while but it always fails a few hours later. Since this happened with two seperate galaxy z flip 4s and two different SIM cards from two different carriers I'm guessing this has to be a common issue with the z flip.