The Nokia Lumia 900 smartphone has been hit with a bug as reported by people on Nokia, Phone Arena, and WPCentral forums. Windows Phone on the Nokia Lumia 900 loses data connections if the cellular link is restarted at any point. This problem also includes something as simple as airplane mode. You can fix the problem temporarily by booting up the phone without a SIM, shutting down, and then putting the SIM in again. It is believed that the unique phone identifiers (IMEIs) were not registering properly on the data network and AT&T is now taking the defective devices off the shelves.