My wife suggested a new way of dealing with telemarketers. (Actually, she did not come up with it, originally. She just passed it on to me.)
Whenever my phone shows that the call is from another town or city--and I have no friends or relatives there--I simply answer the phone as follows:
"Gooooooood morning! This is Phillip Johnston, and yoooooooou're on the air!"
It has worked very well the two times that I have tried it so far. I was met with stunned silence both times.
(Obviously, this will not work with robocalls.)