Everytime they call me, I pick up the phone and grunt really loudly into the phone and hang up. It cracks me up at the thought of the other person's reaction.
Another thing I hate is ignorant telesales people. They phone up asking to speak to the person who pays the phone, electric etc.... bill, when you tell them that they are not in they just hang up without saying a word.
see when they say that, get in before them and lazily say "no **** off" then hang up