I woke up this morning and tried to make a phone call and could not I had a locked sim. Spoke with Loretta at ATT and she was very helpful in fixing that. She also told me that the closest tower to me on the ATT network was severely degraded and that it was quite possible that my service had been impacted by that tower. While there are 20 towers in our region, the iphone looks for the closest tower just like a computer looking for the closest wifi. Unfortunately my phones have been locking in on a damaged signal. I am not sure that was the problem with my iphone4 which seemed bad anyway, but it may explain why my 3GS was wonky yesterday.
I hope this was helpful