Yeah - biggest problem now is dodgy sales calls, silent or otherwise, from overseas. How about Ofcom start talking to the phone operators to see about blocking these, or at least giving a guaranteed accurate number that is calling rather than 'International' - and if their excuse is that the other country can't provide the information, then just cut those countries off from direct dial calling to the UK until they can provide the information!
Personally my solution when I get one of the calls asking for 'Mr whoever' is to say that "he's just seeing a client out, please hang on a moment" and then put the handset down next to the radio. They usually last about 5 mins before disconnecting, but the best was over seven. I consider this to be a public service as that five minutes wasted by them is five minutes they can never get back, and means a dozen other poor sods won't have their day interrupted. And of course, it gives the call-centre drones a breather.
A similar tactic works with the 'you have won a holiday' automated messages from the US - select the 'hear more' option and when you get to speak to some human let them get started and then tell them 'Hang on, there's someone at the door, I'll be back in a moment' and then leave them hanging until they give up.
It's the only language they understand....