A couple of years ago an friend showed me his way of dealing with spam/scam calls. When he saw un unknown nr on his cid he would pick up before his answer machine did and play a message on his pocket digital recorder instead.
"You have reached the Emergency Response SWAT Team. We have ID'd your location. Pls hang up and go to a secure location." I never had the nerve to try it myself - don't know how legal it would be, but he claimed it cut down on his scam calls.