if you really want to mess with them, do *69,
then go to ALta Vista or some similar site with a reverse lookup capability that will give you the name and address of the person calling.
then call the police, call the telephone company and report them (even though they won't do anything, you get it on the record),
then call the person up and when they answer the phone (assuming it is the same voice), address them by their first name, tell them you know where they live, and that you have friends that will rip his lungs out for kicks if he calls again.
i did this, and the nasty calls stopped promptly!