My phone has been working great up until this morning. I got a message "No SIM card installed" when I went to answer a Yahoo message, and next to the wifi signal on the top instead of the AT&T signal bars it has "No SIM". I turned it off, waited a few minutes, turned it back on and it was fine. Now I went in to make a call and it says No Sim again. I will probably take it to the ATT store this afternoon but was wondering if anyone else has had this problem. I'll sync with itunes before I leave so I don't lose anything in case they need to reset the phone.