Try this if your phone fails to ring during incoming calls.
INSTRUCTIONS & INFO
If you recently transferred your landline phone number, you will continue to receive incoming calls on your previous service until the transfer is complete (about 4 days). To check transfer status, visit att.com/port.
Make sure your Wireless Home Phone device is NOT connected to your in-home phone wiring.
Make sure your home phone has power and is properly connected to the Wireless Home Phone device.
The Wireless Home Phone device may be set to forward calls. Dial #21# to turn off call forwarding, if it is currently on.