I have a 16GB 3GS that has not been jailbroken or unlocked ever. Occasionally I look at my phone and see the no sim message when there is a valid sim in the phone. Nothing will fix except for popping the sim and putting it back in. Airplane mode or a reboot wont fix it. Is this is a phone issue or a sim card issue. Another issue that may be related, I have great ATT service where I love but at my office I have 4 to 5 bars but get excruciatingly slow performance including failed sms messages, but at home I have the same bars, but speeds are great. Could this be related to a flaky sim card or do I need a new phone?