So today I received a replacement 6S Plus. Everything went smoothly but when I received the new unit it asked me to select a carrier and the phone will be locked to that carrier and that this can not be undone. Now the odd thing is the phone is purchased through the iPhone Upgrade Program, it was originally for an ATT plan so it is model A1634, but I have since moved to Verizon. Is there the potential the phone is now locked? The Genius Bar people basically shrugged at the whole situation and said they think it should be fine, which isnt exactly encouraging.