I have CLI on my 'phone and if I don't recognise the number or expect a call, I don't pick it up.
This one called a few minutes ago, so I left it and did my usual thing - type it into Google and see what comes up. Lots!
Look at just this one reporting site as an example:
http://www.unknownphone.com/search.php?num=02031824568
Be wary, ladies and gents
