My in-laws have ATT DSL in San Francisco, which gave them a Siemens SpeedStream 4100. I was then attempting to attach a D-Link 624.
It's certainly different that setting up with a cable modem.
The DSL required a User Name and Password (initially living in the 4100). This has to be entered into the router (initially http : // 192.168.0.1).
The 4100 was also 192.168.0.1. Bad.
So:
1) Put 4100 into bridge mode (if you do a hardware reset later you'll have to reenter the User Name and Password, when connected directly w/o the intervening router).
2) DLink->Home->WAN
a) Set to PPPoE for the ISP connection
b) Enter the User Name and Password for the DSL
3) DLink->Home->LAN
Select a different IP Address from the 4100. I entered:
a) IP Address 192.168.1.1
b) Subnet Mask 255.255.0.0
ATT was *extremely* annoying. Their customer service wanted $99 to tell me the settings for the modem/router to hook up to their DSL service. This is what I came up with after Googling and some trial and error. I hope it saves someone else some pain and that $99.