Fax-Spam -- What Can One Do?

phoneAlone asks: "Recently a friend has moved into a new home, where his phone number was previously used as a fax-line and receives a frequent amount of faxes all hours of the day and night. Attempts to contact the senders of this "fax-spam" and be removed from these lists are unsuccessful. What is your experience with fax-spams? What actions (legal or otherwise) can be used to combat this?"