Just register your phone no's with the Telephone Preference Service (and your postal address with the Mail Preference Service, too, while you're at it)
They've reduced junk via either method by over 99% for free.
And how I deal with cold callers like this...
"Hello I am calling because your phone number has been selected to receive a free mobile phone..."
Don't you just love these people?
Well I do. In fact in a perverse way I almost welcome their calls. The reason is fairly simple but first a little background on telesales and how it works.
Company X wants to sell its latest nanowidget and so it hires some dodgy telemarketing firm to ring hapless people who are foolish enough to have telephones in the hope that they will buy some nanowidgets. The way (as I understand it) the money is made is the person making the call will be on commission so it's in their interest to either get a sale or turn a dead-end call around ASAP so they can get onto the next one which might turn out to be a sale. Usually a computer makes the call rather than the person then when the call is answered the computer routes the call to the next available operator which is why you sometimes get those silent calls when an operator isn't available or the computer misfired. When an item is sold the telemarketing company get s a cut out of which it pays the operator who made the sale, ther phone bill and pockets the rest as profit with the remainder being passed to company X as a sale.
So it's all about a shotgun approach - call as many numbers as you can. Terminate dead-end calls as quickly as possible and plough through as many as you can because the percentages say you'll get a hit in every hundred calls or whatever. If they can't get those calls out of the way fast enough they're directly losing money (they still have to pay an operator something and pay the phone bill for the call and they will have given expected figures to company X for sales which they're under pressure to meet).
Now, this is why I actually like getting telemarketing calls...
Whenever someone calls to try and get me to buy something I say "Oh, hello, how are you" and they say some greeting stuff and begin their opening script. "Hold on a second," I say, "you really need to talk to my (brother/sister/wife/mother/grandfather/cat/milkman) about this as they always deal with this. Just hold on a moment, I'll get them for you".
You're now at the most important point of the call - the point where you put the phone down (DO NOT hang up, just lay the handset down on the table with them waiting. From this point on you are losing the operator commission, losing the telemarketing company potential revenue and running up their phone bill.
"How do I know when to hang up?" you may ask, and a very fair question it is, too. You know when to hang when phone makes this noise:
If everyone treated telemarketing calls like this then pretty soon no-one would ever have to worry about receiving one as there'd be no telemarketing companies left.