You have two modem/router choices for the AT&T Internet Uverse plan: Motorola NVG510 or the Motorola 2210-02-1ATT. The NVG510 doesn't have a bridge mode, and there are a wide variety of hacks to use the IP Passthrough option for the Motorola NVG510 modem:
If you read through the discussions though, you'll notice that the discussion gravitates towards using the IP Passthrough with a Fixed-DHCPS set for the router's IP address: "i'm using the IP Passthrough functionality. According to its own instructions on the right-hand side of the tab, the RG is supposed to pass its public IP address through to another device, using its own DHCP - but it won't do it. I had to manually enter the information into my regular router (an Airport Extreme Base Station, aka AEBS) to use the Passthrough functionality.
...it seems more better if you had a choice to go with the Motorola 2210 option. Also, don't confuse the Motorola 2210-02-1TT model with the Motorola 2210-02-1022 model, the latter of which was an old DSL modem that you can buy off Ebay. For one thing, the 2210-02-1022 models only speak PPPoE, and since the Uverse solution relies on authentication based on the MAC address, you won't be able to plug this modem in place of things. You can check your diagnostics tool on the router to verify that you're connecting via IP-DSLAM, which is synonymous with the AT&T Uverse Internet 18Mbps solution.