Have you tried putting it into airplane mode then turning off airplane mode? I dont get cell reception in certain parts of my office building and I find sometimes it takes a while to find service again when im outside, that usually fixes it for me. Not sure about any technical issues but it may be an easy solution
Thank you for your help. And yes I forgot to mention that I have tried turning off and on airplane mode. I once even reset network settings and that fixed that problem that time.
But the problem keeps on happening intermittently once I come out of an area that doesn't have any signal like the subway in New York city. The first time it happened I thought every customer using an AT&T iPhone must have lost signal because that was the first time I experienced something liked that since upgrading to the iPhone 4S from an iPhone 3G.
Something you can try is restoring your iPhone. If that does not work most Apple products come with a 90 days of free technical support. You can speak with someone online by following the link below or by making an appointment at an Apple store. Unless someone else here comes up with something else that might be your best bet.
When you enter your serial number in the webpage below it will tell you what your eligible for.
To find your serial number go to Settings>General>About