When I get calls on my landline it appears on the TV, when I see it is a telemarketer I press what ever number it requires to reach live person, I take the phone and put it up to my parrot's head, when he hears the voice he starts talking to the telemarketer, after few mins they get frustrated because my parrots answers don't fit the questions for some reason.
Example
Telemarketer "Hello" is so and so there"
Parrot " Hello how are you?"
Telemarketer "I am fine thank you, I can help you lower your debt"
Most a computer generated calls, if there is a hello from your end-then the marketer come on. If you pick up and not say anything it just disconnects after 5 -10 seconds.
I have had even a return call many years ago - stating that I had a "Potty Mouth"
I try not to asnswer telemarketer calls, but now and then one gets through. Just tell them to hold the line for a second and walk away. After ten minutes hang up the phone.