We have made it a habit to never answer the phone if we don't recognize the number or the caller I.D. If it is someone we know they are invited to leave a message and we do return calls. Our VOIP provider also lets us block repeat robo callers.

If you want to be entertained, answer the cal and have them repeat a lot of stuff and ask totally unrelated questions. The object of the game is to keep the caller on the line as long as possible. A friend who recommended this tactic kept one caller on line for 20 minutes.