The Federal Trade Commission, which oversees the government's do-not-call list, announced Thursday that it will offer a $50,000 prize for the best technical solution to block illegal commercial robocalls.
I think some phone answering machines can answer each call and require the caller to press a number for the call to go through. The robo machines can't press a number they don't know.
Or just have the hired help screen your calls for you. lol