ATT Digital Phone

What have you tried? Assuming you can make outgoing calls try resetting the modem.

Is this for new phone service just being setup?

if yes activation been completed?

You have the option of activating your Voice service either by calling or going online. A Call 877.377. 0016 from the phone connected to your Wi-Fi Gateway and follow the instructions to complete activation.

https://www.att.com/media/att/2015/support/pdf/ATT150430905_UV_Voice_Add.pdf

other possibilities if was working previously include Do Not Disturb and Call Forwarding to different number.

Digital Phone - Do Not Disturb Call Feature

We understand that some of our members are not receiving phone calls. This could be related to a feature known as Do Not Disturb. This feature prevents all incoming calls from ringing through, giving callers a busy signal. In some instances, this feature is turned on inadvertently.

You have two options to setup this feature:

Using Your Home Phone

To turn on the Feature Dial: *78#
To turn off the feature: Dial 79#

On The Via The Customer Portal

1. Go to the Online Portal.
2. Scroll down until you see Featured Controls.
3. Click on Do Not Disturb.
4. Select On to enable the feature, Off to disable the feature.
5. Select Save.