Depending on where you are at, it is more than likely a network issue. AT&T wants people to buy data plans and data devices more than anything else. The sad truth is that the AT&T network is not ready for mass amounts of data users. The increase in iPhone data users, as well as the influx of other devices that use massive amounts of data, has really bogged down the system. In some cities it has become almost unbearable. The worst areas are southern California, Chicago, New York and the D.C. area. Even in areas that are smaller population wise, they still have had a rise in data use, therefore spreading the issue out into the fringe areas as well. This seems to be mostly in the 3g area, but it does hit into some 2g areas as well. I myself am losing calls and getting massive delays on the messages. Best bet is to keep reporting it to them and see if that lights a fire to get them to change things.
10 + years in wireless industry, and a good long conversation with an AT&T network field worker.