I live in the Los Angeles area where the AT&T coverage is good for LTE as well as 3G. My new iphone 5 will lose connectivity to the network at least 4-5 per day and say no service for 1-2 minutes then come back at full bars. This is not happening when moving around or anything but just at random times. Is this a known problem for iPhone 5 / iOS6? Or do I have a defective device?