dial-in access to linux server

I have a Redhat 6.2 machine with 2 NIC cards. One to a local hub for other pc’s, and one to my cable modem. The linux box uses ip masquerading to allow the clients on the hub to get access to the internet. I want to install a “telephone” modem into the linux box, and configure it to let me dial in to get access to the internet. Sort of my own “mini-ISP”. Is this possible? Any clues as to what software I’ll need to use to answer the modem, and allow traffic from the cable modem to the phone modem?