They've been driving me crazy night and day, too.  Two suggestions: first, if its someone like these creeps and you want to redirect the misery, go to the dollar store and buy yourself a plastic whistle (like coaches use). When you see that number come up on your caller ID, pick up the phone and blast them with your whistle. You have no idea how good it will make you feel.  Second, an experiment I'm getting ready to try.  There is an archive of telephone recordings at http://stuff.gigo.com/phone/
Since most telemarketers use a computer to dial for them, I think that making a new message on your answering machine that begins with that earsplitting "the number you dialed has been disconnected"  tone might make the computer hang up.  If we're really lucky, the computer will log your number as having been disconnected and they'll never call again.  Its worth a try, anyway.