I restored and updated my iPhone 3GS to iOS 5 and I receive the "invalid SIM card" error. I replaced the SIM card and AT&T ensured me that wasn't the issue. I haven't jailbroken my phone, but I hear that may be the only solution? I'm stuck at the "invalid SIM card" screen though can go back to the "Restore" screen, but those are my only 2 options. Therefore, I'm unable to find out what the firmware is or any other details. Please be very descriptive with the steps for possible solutions! Thank you in advance!