How to Fix iPad No 3G service after 4.2 upgrade

After upgraded to iOS 4.2.1, my iPad 3G + WiFi got the following symptomsWi-Fi worked fine, but the network status indicator didn't show "AT&T 3G", just "No Service". In the settings, there was No "View Account" button on Cellular Data. And "Unknown" carrier and "Unavailable" cellular data number showed under "About".How to fix No 3G service after upgrade* Tap the Setting and turn "Airplane Mode"