Screening calls with a Modem

I have a pile of a modems, and a ton of telemarketers / general idiots asking for tech support, and I'd like to stop them from calling by somehow blocking them with with a spare computer. I'm wondering if it's possible to slip a computer running any OS between a jack and a phone, have the computer recieve the call, check the caller ID from the first ring, and if it doesn't appear in a blacklist, ring the phone. Otherwise, disregard the call, and pretend it never happened.

Is such a thing possible, using spare parts?

I guess you must have advertised your expertise.

My solution is to ask for their VISA number at the start of the call. Repeat the request as needed. Tends to discourage free loaders.

Seriously I need the same system, especially on my fax lines.

I am willing to pay $ for such a system.