I have had this problem with SIM cards in the past. The issue is with the SIM card not being coded correctly. You'll need to call your carrier (mine is Cingular) and ask them to "refresh" the SIM card. Be advised they may ask that you have the device in front of you as they typically try to have the device OFF before they send the Refresh command through the system. That way when you turn on the device, it will be sure to get the refresh when the device comes up for air.