First I called and made sure to register my MAC address with AT&T. This is necessary but unfortunately not sufficient to get things working with Linux.

Of course, Linux is unsupported, but I thought it would be easy enough. After days on mailing lists, trying to figure out how to make things work, the solution was to install dhcpcd (which I couldn't find with apt, so I downloaded the deb for it and did a dpkg -i on it. That required me to uninstall dhcp-common and pump.)

With dhcpcd installed, I just had to run dhcpcd -h my_subscriber_number -d. The -h flag tells dhcpcd to use my_subscriber_number as my hostname. This is the magic trick that lets AT&T's DHCP server give me an IP address.

In retrospect, I'm not sure if -h my_subscriber_number was necessary. However, I'm pretty sure using dhcpcd rather than dhclient was important.

Here are some useful links:

• AT&T's DHCP help page
• dhcpcd manpage
• DHCP mini HOWTO

I update this when I learn how to make it work with dhclient, but for now I hope this helps.