This app pops up when you call numbers that aren't normal UK landlines or mobiles to ask if you want to continue. It's not just 0870 you need to worry about!
Unlike similar applications, this doesn't need you to maintain a database of lookup numbers. There is just one number to redirect to that should take care of all numbers. You can easily change this too!
Comes with no warranty of knowing about every expensive number.
Note that this is an application for the UK phone market.
This is an extension to the original Number Check (https://market.android.com/details?id=uk.co.laurencea.uknumbercheck) that allows you to choose to redirect the call to the default http://www.0800Buster.co.uk number. This can be overridden in the preferences screen.
Note that this code may get merged back into the original application.