I love unsolicited sales calls. I have a "home" number which gets no such calls (registered with the appropriate authority), so I get the unsolicited ones on my "home work" line, a remnant from my previous job. I generally rotate between three actions in response:

a) speak Greek to them
b) leave the handset on the table as long as it takes; I don;t care, very few people know that number anyway (and Villan, you are asked to forget it herewith!)
c) I talk agitatedly along the lines of "my dog just stopped breathing - do you know about dogs?"

But I mostly speak Greek. I like the idea that my mother tongue is being heard in some remote corner of the world. If I do it enough, they might learn it.