Ok that's for the reply. This issue doesn't seem to be affecting all S3 and some seem to be fix (or people just got a different phone) but I can't find a solution. I have gotten the phone and sim card replace in mine and my wife's S3 and still have the problem.
I ditched the S3 due the fact no one could tell me what was wrong and I had dropped 7 calls with in about a week and a half. My SD card was formated prior to being used in the phone so I don't think that was the issue. I had the phone replaced and a new sim card which didn't help. I now have the Droid Razr HD and have not had any signal issues or dropped calls and most of them were made at or very near where the S3 failed. In my opinion the S3 is a great phone if you line under a cell tower but for me I'm constantly in and out of 4G coverage but always in a 3G area. The S3 can't seem to switch properly and when I took it back to have it replaced again I was even told that quite a few come back for that same issue. I find it really weird that those phone have that poor of signal reception and people are returning them and calling tech support constantly yet version nor Samsung acknowledge the issue!!
Yeah I'm passed!
Rant off. ;-)