I have an Asus RT-N16 router that I have installed Tomato USB on and have been really happy with over the last few years. We moved to a new apartment recently and ended up using AT&T U-Verse as our internet provider. Now AT&T makes you use their own modem/router and we got stuck with a 2Wire 3600 HGV. I frequently do geeky fun projects (like setting up a VPN on my router, or streaming our security camera onto my iphone) and wanted to keep on using my Asus Router for better control. So I spent the last 2 days figuring out how to do this, and the steps are documented below.

1. Log into your own router and change its IP Address range so that it does not conflict with the U-Verse router. On the TomatoUSB admin page, I can go under Basic > Network to do this. I changed the router IP address to 192.168.2.1 and the IP address range to 192.168.2.100-192.168.2.149. Connect the WAN port to one of the ethernet ports on the U-Verse router.
2. Log into the U-Verse router admin page. The default IP address for that is 192.168.1.254. Under Settings > Firewall > Applications, Pinholes, & DMZ, select your own router and under “Edit firewall settings for your computer”, select “Allow all applications (DMZplus mode)”.
3. Reboot your own router. It should now pick up your public IP address and be good to go.