I had this bookmark that has since gone, but what it was an experiment run out of finland or some such European country which aimed to reverse the balance of the call in order to solicit information out of the telemarket.
They had a flow chart you went through, and it worked seemlessly - immediately you'd become the one asking the questions, and you'd ask about how they got the number, what company they called from, and just before the end it had some token question about how much they earnt and what toothpaste the recommended. It even had a "if your telemarket gets irate" box with courtious replies. You were meant to fill out the form and send the creators the answers. Bag of laughs and it worked amazingly, they stopped calling our house after about 3 runs through.
Although, since working on a helpdesk, i've learnt that it's sad to fuck around with the people on the other end. I've also noticed at uni that there are heaps of fliers around advertising for the job late at night for desperate students. So remember the next time you get one, this person is probably just desperate for cash and would really rather be at home enjoying a lovely meal like you are :P.
I need to find that site again.
[edit] Found it!!
http://www.xs4all.nl/~egbg/counterscript.html enjoy :P [/edit]