Thanks.
so it is all about call termination charges? but how can then (as an example) davegr provide a number inclusive on most networks you can use to make international calls including expensive destinations. surely someone has to pay for that call?
Yes it's all about the MTR (mobile termination rate). If for example a number range has a termination rate of 3p per minute, then you could offer calls to any destination with a wholesale cost of up to 3p without losing any money and calls made to cheaper destinations would make you a profit.
As for how I am able to provide such a service on a number that is inclusive from all networks - that's something to be explained another day, in a more suitable sub-forum, maybe....