Okay here is my story...
Purchased my phone on Nov 4th nothing but problems with coverage. AT&T support reset network,replace sim card and finally restore phone to receive "tweaked 5.0.1" update. Nothing worked keeps searching for signal.
Replaced phone worked fine for 24hrs then the dreaded searching for signal error came up again.
Replaced sim card still acting up!!!!
Okay dig deeper.....
I noticed that my sister asked me if I received a picture she had sent which I did not.
So she sent it to me again and low and behold I lose signal.
No really!!!!
Asked her to send it to my wife same thing she lost signal.
Okay the fix.
With iMessage turned off the iPhone could not process the picture and in the process I lost signal
Turned iMessage on....... Shazaam problem solved.
Hope it works