Tired of credit card/personal loan/real estate solicitations?
The primary purpose of any response to a telemarketer should not be anger or criticism. It should be to waste their time without wasting yours!
The most effective way of doing this is to simply express interest, ask them to please hold for a minute or two, press the mute button on the phone, and then ignore the phone for some time. And if you can come back once in a minute or so and say "just 1 minute more please...", all the better!
If enough people do this, we can make a big impact on their moronic employers. Please pass the word.
Alternatively, you can trade time for entertainment and actually talk to them. Ask them about themselves. Their job. What do they get paid? Does their family like it?
Be genuinely curious and interested. And friendly. Don't get angry or insulting. They'll just hang up and move on to the next victim. You have to keep them busy.
Sometimes you get a real idiot. My favourite is when I confused the heck out of one poor girl by asking her to punch in her ATM pin code in order to be able to speak to me about my (non-existent) credit card! I told her until she does that I cannot believe that she is who she claims to be. [She punched in something but then she hung up.]
But all these methods require you to be engaged actively, instead of just letting your telephone be busy for a few minutes. For calls while at work, nothing beats telling them to please hold on...