I had a roommate in college who was great at this. One of the things he used to do was keep one of those freon horns close by the phone. Anytime he'd answer a telemarketer he'd get 'em talking, then let out a blast with the air horn right into the phone. Then, he'd say, "what the hell was that?" After a few seconds the telemarketer would go back into their blather and he'd give it another blast with the horn. Usually, it took 4-5 blasts before they got the message.
I really hate telemarketers. My home phone is unlisted and is never given out to anyone but family. I use my cell for any contacts that I might need. I'm on the national and state "do not call" lists, we've registered with the National Association of Telemarketers (or whatever they are called) on their do not call list, and with all that we still get a half dozen telemarketer calls every week. I pay for the phone access to my home and that makes it my property. I view telemarketing nonsense as trespassing and an invasion of privacy, not to mention a waste of time because, simply by virtue of you making an unsolicited call to me, you have removed any chance of me ever doing business with you. That's been my policy for over 20 years. You'd think they'd get the message, huh?
So am I. I see more and more calls from boiler rooms in Ontario. Also, "Charities" are exempt from the lists. If you ever give to one, the number hits the suckers lists.
The worst offenders are the so-called "Police and Fire" charities, where the locals might get a penny out of the Dollar. The local Police run warnings in the papers about them.
We have record low unemployment. There is no reason for anyone to be a telemarketer, and limited sympathy for them. Intruding into people's quality time will get you part of what you ask for. This includes suppertimes.