Vbox3 can answer phone calls on isdn lines, and also initiate phone calls itself. in a simple configuration it can act as a answering machine, playing and recording messages, recorded messages are forwarded through email. with the help of the raccess4vbox3 package it's possible to create a complete voice response system, with dtmf touch-tone support, navigating through menus, and even remote controlling your debian system.

see http://smarden.org/pape/vbox3/ for details.