Try this if your phone fails to ring during incoming calls.
INSTRUCTIONS & INFO
Transferring a phone number can take about four days, so you should keep a phone plugged into your wall jack to receive calls on your old service (including 911) until your transfer completes. However, you can make calls immediately on your Wireless Home Phone device. Check transfer status at 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.