We are on call preference at home and when we get the odd cold call, I tell them that they are obviously a c**p company in financial trouble as they can't afford an up to date data base and the sales person should maybe thing about looking for a new job as the one they have will not last long.
They very rarely ring back.
At work I ask " who's calling" this always seems to through the Indian's off their script, if they tell me I then ask them what it is regarding, this normally confuses them even more, when they tell me, I say I am not interested and not to call me again.
When they do, I ask again "who's calling" and then say I will just put you through, lay the hand set on my bench and carry on with my work and about 5 mins or so later hang up.
The really annoying ones I have had recently is due to the fact my van insurance is due and a couple of years ago I used a comparison site, and my data has obviously been sold on.
I will never use a price comparison site again.
Tom