Report from their site:
We are enhancing your online experience, and myAT&T is temporarily
unavailable. We apologize for the inconvenience.
If you need immediate assistance, please contact customer service at:
Wireless: 1-800-331-0500 or 611 from your wireless phone
U-verse, Phone and Internet: 1-800-288-2020
During this time, hold times may be longer than normal.