Check out Device Support tutorials and videos that'll teach you how to:
Turn off Airplane Mode. Most phones display an airplane icon when Airplane Mode is on.
Turn off Do Not Disturb or Quiet Hours. Some phones have this setting to keep you from getting calls during certain times or while the setting is turned on.
Turn off Call Forwarding.Press #21# on your phone and then the Call, Send, Talk, or Receiver key. If your calls continue to forward to another number, learn how to turn call forwarding on and off.
Check the Blocked Calls or Reject List. On some phones, you can block calls from certain numbers or create a reject list to avoid calls you don’t want to get.
Insert SIM card.Steps on how to remove and reinsert the SIM card if your phone displays Insert SIM or Emergency Calls Only.
More troubleshooting tips
Visit att.com/softwareupdates to verify your device has the latest software and update if needed.