When that happens, you might see the "your phone is not registered on a network" on your screen, which means your SIM card can't connect to your wireless provider's network.

To check if your Android phone is unlocked, try swapping in another SIM card or test your network settings. If calls work, ...

If you don't spot a connection in the status bar, try ejecting the SIM card tray and inspecting it and the SIM card for any damage. Reinsert it and reboot your phone to see if you have network ...