Cheap B*stards

As if normal telesales phone calls are not bad enough, with almost incomprehensible sales people from half way around the world trying to sell the undesirable, now these affronts to privacy are trying to cut costs. Over the past few weeks I have received several phone calls that, when answered instantly hang up. Using the rather useful BT feature of 1471 to find the last number these calls originate from 0845 (local call rate) numbers.
Being the inquisitive fool that I am I recalled one of these numbers to be confronted by some foreign voice trying to sell me double glazing. Do these companies really think that I would even consider buying their product on the basis of this; even if I wanted what they were selling in the first place.