So I see many had this error with old iphone. I got my 3G 2 days ago. Since then, I have had the phone all of the sudden display "NO SIM CARD" Message at the top where it should say AT&T 3 times already. Each time, I pick up the phone to make a call and I discover this message. I reboot by pressing the top button and home button at the same time. The problem goes away each time. But comes back in few hours. Is there another way to deal with it, other than to do a reboot like I am doing?