My son and his wife got me a wondeful gadget called The Butler. It plugs into the phone jack then you plug the phone into the gadget. When you press the * key a voice comes on - in a very proper British accent - "This is the Butler speaking, this residence does not accept unsolicited --- etc ---" winding up by saying I want to be removed from their list. According to current federal law if you ask they can't call for a year. Oh, and the gadget works on all extensions with the same number including cordless .
Only problem was that a telemarketer called me back and asked where I had gotten the Butler- she loved it! And -get this - wanted one for her home phone!
We had a thread ages ago about ways to frustrate telemarketers perhaps someone much cleverer than I can find and post link? !!