Connecting Time Capsule (or AEBS) to a AT&T U-verse Router/Modem - Proper Settings and Setup?
First, connect one of the Ethernet ports of the 2Wire Gateway to the WAN port of the Time Capsule and turn both devices on, and disable wireless on the 2Wire. Your Time Capsule settings should not be changed from what they were when you had things working with your cable modem. If you've changed them, change them back now.

Then, on the 2Wire Gateway, in the "LAN" section:


Enable DMZ for the Time Capsule connection
Turn off the firewall for the Time Capsule connection
Set the Address Assignment for the Time Capsule connection to "public"
Set the WAN IP Mapping for the Time Capsule connection to "Router WAN IP address"


Then cycle power on the Time Capsule. The Time Capsule will now control everything just like it did when it was connected directly to your cable modem. Any wired Ethernet connections you add should be connected to the Time Capsule, not the 2Wire Gateway.

FYI, this works for any router or access point, not just the Time Capsule.