I am of the opinion that the people calling are just making a living. I stay on the line and ask them to take my name off the calling list. It seems to be helping.
We have many callers from out of country, so I ask to speak to someone in my own country, and ask them to take my name off the list.
If there is any hesitation, I ask them for their home phone number and the home phone number of their supervisor. They usually ask why, so I explain that I'd like their number so I can invade into their personal life.
Slowly but surely the number of calls are diminishing.
I also rarely answer 1-800 numbers. I too am of the belief that if it is urgent they will leave a message.
amh