I have had crappy jobs so i am always slightly sympathetic towards telemarketers - cos basically what most of them are are normal people with a crap job they probably hate.

I have come up with my own script which seems to work fine, with the minimum fuss though.

Them: Hello, can i speak to....
Me: Who's speaking please?
(repeat until answered - company name please!)
Me: And what were you calling with regard to?
Them: blah blah selling something blah
Me, I'm fine thank you. Have a good day. Goodbye! (firmly but in a friendly tone)