Mike,
I don't know if this device works, however....
On a recent radio talk show, there was a gentleman discussing the telecommunications privacy act. This act prohibits unsolicited faxes as well as calls. Once you receive a call and request to be removed from their list, they are prohibited from contacting you again.
He seemed to have made a living by threatning suit against these repeat offenders. He had collected somewhere in the neighborhood of $40K in one year alone.
It is my understanding that for each subsequent infraction after you ask to beremoved from their list they are liable of a fine of at least $500.
This guy documented everything on paper [from what he said, this was acceptable proof if it ever came to court. ] He also kept copies of all unsolicited faxes.
He contacted the companies that made subsequent calls and offered to settle with them for somewhere around $300 each.
According to him many telemarketing firms have set aside a fund for these types of settlements.
It is my understanding that them paying the settlement was cheaper for them in the long run than stopping the calls.

The radio show i'm talking about is called "Tom Martino the problem solver". It runs in the NY area weekdays at 11AM EST. He had the info on his website for a few weeks early this summer, unfortunately I can't remember the site address.