I think it's done with a microcontroller... Have you tried searching the web about how it works? It would be cool have a caller ID modem, you could keep a log of unwanted callers, and have the computer dial them back or answer, with "Quit calling me" message. It could also automatically screen out such calls. Really hate those 'Congratulations!' calls, they fill up the answering machine, telling me about the wonderful timeshare opportunity in central Florida... I already own a house, near all the attractions!