So I have had this iPhone for about 4 months now and it's been working fine up until yesterday. It is an iPhone 3GS (ghetto, I know) for at&t that is jailbroken and unlocked and I'm using it for Tmobile. Now, it randomly started saying Invalid SIM in the status bar, or No Service, where I know it has service. I know this is an old problem that a lot of people have had, but could someone pleaaaase help me? I've toggled airplane mode, turned off my 3G, reset all network settings, rebooted the phone, uninstalled and reinstalled Ultrasnow and the Ultrasnow fixer several times and absolutely nothing is working. Any help is much appreciated!