The next time you get offered an 087x number - or the first time you call one - ask for thier Platform Number - this is the actual number to which the 078x number is attached. They seldom refuse point blank to give this - and then you can phone them cheaper (or for free if you have an all-in deal from you phone compnay). This is, of course, also true for 0845 numbers, as these are not always included in your phone provider's all-in deals.