Searching for AT&T signal constantly after iOS 5.1

[NorCal 98]

After I updated to ios 5.1 on 4S my service thru AT&T which was perfect is now
Losing signal literally every two minutes. It will show full bars and 4G and work
Great for about 1.5 minutes then signal starts fading and then it goes to searching
I've tried hard reset and even reset and set up as new phone. I've been searching
since the day the update was released and haven't seen any other threads that match
the same problem. It's wiping out my battery life. Anybody else have this problem
Or have any ideas. Thanks

 

[mutludeli]

Im using 4s unlocked and i dont have any problem, But
my frient he is using locked phone by operator in BULGARIAns MTEL, and he has the same problem with losing the signal.
What he sould do ?

Also one more question?

is this problem is caused because of the micro sim card or becuase of the operator ?

 

[pollo_pollo_uk]

I am also having the same issue after upgrading to ios 5.1 - AT&T signal goes to searching or no service. It was absolutely fine prior to the upgrade. Does anyone have a fix yet?