I have an iPhone 5 running iOS 6.1.2 on AT&T. I've noticed I am unable to use my Apple ID for both Facetime and iMessage; if I am signed in to one of them, I'm unable to sign in to the other. I get in a loop of the phone repeatedly popping up a password entry screen for the Apple ID. If I cancel the process and sign out of either, I can successfully sign in to the other. But no matter which I sign into first, I cannot sign in to both at the sametime. >__< Any ideas on a fix? It's driving me nuts.