No clue about BellSouth, but on the left coast, AT&T has been using
2wire 2701HG modems.
In my never humble opinion, there are very nicely built and fairly easy to setup modems. Punch in the proper code:
and it's ready to install. Security is setup by default using a WEP/WPA key printed on the serial number tag. I believe the current models are delivered with a WPA key. If you get one with a WEP key set, I suggest you change it to WPA and a longer key.
Some wonderful person was good enough to provide an online emulator at:
which should be adequate to give you a preliminary tour of the setup. It's not perfect, but close enough.
It would probably be a good idea to ask the customer what they are using.