Telephone numbers displayed to people receiving calls must be valid, dialable and uniquely identify the caller.
How will that apply to international calls? A lot of countries can't/don't/won't supply CLI last I heard. Of course banning those will cut out a fair bit of 'spam' but enforcing it will also block legitimate calls from large swathes of the world.
According to Wikipedia very few countries do (which I find a little unlikely) and don't follow the same standards (which sadly doesn't surprise me).
Biting the hand that feeds IT
