I get a few calls from numbers such as 08700426655 that are from cold calling center's. In the past I was annoyed with these numbers, well to be honest I still get annoyed with these numbers. What I've done though is put these numbers into my mobile under “Don't talk”. Whenever I get a call from these numbers now, I answer the call but don't say a word. I wait on the line until the caller hangs up. Usually these companies ring 6 people at the same time and hang up on 5 when the first person answers. So when I answer I save 5 other people the hassle of talking to these morons and secondly I waste their money and time while they try and get me to talk 🙂
Now all I need to do is register an 0870 number with them and get them to ring me several times a day!