I think you have to sign up on the "Do Not Call" registry every few years. It also only stops calls from "unknown numbers" IF, and I stress that word, IF the people calling even get the list and go through it to see who doesn't want to be called.
Called 11/21/2012 at 10:55 AM. I got the last half of this call on my machine asking me to support impeaching President Obama, and offering a free "Don't Tread On Me" flag if I donate. The removal number at the end was read so fast I had to play the message twice to make sure I wrote it down correctly. The removal number (877-705-6767) belongs to the "Conservative Majority Fund."
John-I saw your post that you received a message from the Conservative Majority Fund too. Thank you for providing their telephone number to ask to be put on their Do NOT Call list. I answered the phone and the caller spoke so quickly, I could not get the # but your post gave it to me. Calls with that kind of message are more than infuriating-hope however runs this site does something (altho' doubtful).