I switch my Verizon 5S to ATT just less then week ago. Absolutely seamless. Only what they did is put different phone ID in their system (brought new 5C and put that ID) because according to the guy it did not accept it. All works perfect, call and LTE. On my page in ATT it doesn't know what my phone is however. It shows my sisters ATT iPhone 5 correctly. It doesn't show my wife's Verizon Note 2 correctly also, but phone works fine after two, almost sleepless night messing with APN settings and listening her voice that if I will not make it work she will get a new phone soon.