Each day at random times my phone goes out stating Sim card not found. i was hoping there was a fix in todays update but of course no update. i have been travelling so i cannot back up etc. I have done the reset, the hard reset, and plug into the electric cord, and eventually it does come back but i miss the calls, messages etc. which happen durring this period. What is the fix for this?
Have you tried removing the SIM and reseating it? If you don't have your official Apple tool with you then you can use a paper clip. If that does not work then you may need to get a new SIM from AT&T.
If it is an iPhone 4 it is on the side. Bend a paper clip, insert it into the hole, push and the tray will come out. Pay attention to how the microsim is seated and be sure not to bend or damage the tray.