http://www.saynoto0870.com

Enter the company name or the 0870 number you have into the search feature:
http://www.saynoto0870.com/search.php

this is a great link

does it work with every number

I was very angry when I could not use my free minutes for those numbers on my mobile contract with O2 anymore

It does not work for every number unfortunately.

xx

Please be aware that some companies don't charge you for support when they ask you to call an 0870 number. I use the miniscule amounts from my 0870 to fund the fact I support end users with their problems well beyond their server issues half the time.

0870 to big company - bad, 0870 for a small company - good.