Rather cruel for the telemarketing employee, but genius nonetheless.
A little while ago I put together a little application on our phone system so that when a telemarketer calls in, I can transfer them to this extension and annoy the hell out of them. I thought about it a bit more and decided to make it a little more interesting, so I can get them to hold on the line as long as possible.
Previously: TeleZapper. I have one of these and it definitely makes a difference.
Update: The author admits it was a joke, not a real telemarketer. Totally lame.