Reply "Mushi Mushi, Agangkidisca. If telemarkerter, increase your voice saying it again. then say Mushi once very forceful and loud. They generally hang up. Works very well. It is Japanese for saying Hello, how are you doing! Funny thing, Japanese is one language no one seems to learn. Otherwise, do what we did, get rid of the land line which we did and no more darn telemarketers.
As for going thru a check out line and they are wanting your phone number I generally say no but if they insist, I say for example in my area 540-555-1212 and the bumble heads do not get it. For you see it is the old style phone number request instead of 411 for information. Works like a charm and for the old timers who recognize that one, I generally get some good comments.