Just for fun, if you are working or living in an environment that you could do this in, answer the phone whenever a suspected telemarketer is on the line. If you hear a real human voice and they start their shpeel, hold a gas charged air-horn to the phone & blast them for a second or two! You can get them from amazon.com for as little as $7.00 for the 1.4oz can or under $30.00 for the 8oz which will last a very long time if used in short bursts. Refill 8oz cans are about $16.00. Free Shipping often available on orders over $25.00!
Even if it's a recording, wait and see if a human takes over the call or if there is an option for them to start recording you, then blast them!
Don't get mad, GET REVENGE!