Been getting a number of calls over the last few months, which, when I've answered, have simply hung up. As it's been getting more and more irritating, I'd started to log them in my Contacts, just to see if it's the same number or not.
Well, lunchtime today, the mobile rings. And, sure enough, it's one of these numbers. In this case, 0870 042 6655. So, just on the off chance, I Google'd for it. And I found this:
Having a look through, one recent listing takes you to another blog, and how they've tracked down where they're coming from, and more importantly, why.
Turns out it's a sneaky marketing ploy. They call you, hang up, and you, foolishly, call them back. They make money from the call, and then try and sell you a new mobile.
I'm glad I've got that number in the mobile now, least I know not to answer it anymore 
Thanks for this - just got a call from that number and googled it, found your site. Detestable filth.
Cheers
Bruce