Check out the site coloradonocall.org
you can put your phone number on a colorado no call list that is supposed to greatly reduce the number of telemarketing calls and faxes you receive. It appears to be a legite thing - says they actually fine companies that call numbers on this list. Maybe worth a try anyway...

Solicitation blocking

We have a feature on our phone provided by QWest that plays a little message to incoming calls that says that we don't accept solicitations. You can prevent the message from being played to friends and family by adding their numbers to an exemption list. We haven't gotten a single sales call in 2 years. It costs a few bucks a month, but it is well worth it.