Answer the phone when they call and conference in the Jolly Roger telephone bot http://www.jollyrogertelco.com The bot will waste the telemarketers time, which is the most expensive thing that these companies are paying for. Do this enough times and the calls drop off rapidly.
I've become irrationally irritable because of these calls. I have started subconsciously turning off my ringer, causing me to miss actual important calls. Jolly Roger may be my saving grace.