While working with AT&T over the years configuring Netopia 3300 series routers, the two best tips I’ve heard is:
The hidden configuration page at http://<ipaddress>/setup which provides an overview for just about every inital configuration you’ll want to make as an IT Professional. Typically we set these boxes up with NAT disabled and place our own firewall behind the box, either a Sonicwall or Cisco device.
The second is that it can be critical to ensure that the VPI & VCI are configured properly. I have found them misconfigured on more than one instance.