If you currently have a phone plugged in to the back of the modem, you could run that wire to an existing phone jack to supply dialtoe to the rest of the house. Or you could go to a cordless phone sys ten by plugging a Cordles base station into the modem.
JamesR is correct in running a RJ11 wire from the modem to an existing phone jack. I'd just suggest however to make sure that your old connection to the AT&T landline system has been disconnected first.
Thanks for the reply. I like the idea of a cordless phone system and not messing with the AT&T phone jacks.
So... the way to do it is to go purchase a cordless phone system (that has the amount of extra phone handsets that I want) and just plug the base station phone line into the back of the modem and then it probably has an electrical cord that I need to plug in also. Set up it's optional features such as preferred language/amount of rings/etc...
Then place the extra phone handsets in the rooms that I want them in, probably having to plug their base into electrical outlets, setting up each phone handset with their optional features and that would be all I need to do?