I do not know how much a "TELEZAPPER" costs new, But one was given to me as a gift.
THEY DO WORK WONDERFULLY.
When someone calls they hear a tone and each time you pick up the phone you hear the tone.
It is a little annoying at first, But you get used to it. Family will ask what "it" is but once you explain what it is they have no problem with the tone.
It ELIMINATES calls a second time from the clowns. Darn, I miss playing with the telemarketers and saying "Thank you for calling prime credit USA, Peggy speaking....
Maybe I should disconnect the ZAPPER ? NOT !