For some reason, my phone keeps telling me I have no SIM card installed. Each time I will eject the SIM tray, make sure the SIM card is securely in it's tray, and then place the tray back into the phone. The phone is happy for awhile and then will tell me again. I have an iPhone 3G on ATT in the United States, if this helps to diagnose. Thanks in advance for anything anyone can tell me.