I have a new iPhone 5 AT&T. About 1 out of 10 times when I leave one of the two wifi connections I use daily (home, work), it will not make the data connection to LTE/4G properly. The LTE or 4G indicator shows connected and I CAN make phone calls, but the data connection will not work until I toggle airplane or cell off/on. After manually toggling cell off/on, it works fine. This is an intermittent problem. I searched but didn't see this exact issue being discussed. Does this sound like a device or AT&T issue? Should I exchange the phone?