I updated iPad and iPad 2 several days ago. Yesterday my iPad 2 went No Service then Invalid Sim. After a full reset and restore from iCloud it was the same - no service and invalid Sim. AT&T store replaced the Sim and it worked for a couple hours. Last night my iPad 1 went No Service and my iPad 2 has the AT&T bars but no 3G or Edge. I can connect through wifi but there is no 3G data connection. Any thoughts other than a visit to the Apple store?