formally spoof cellphone number

[Lope]

When I say formally, I mean fill in a form or whatever is required to have it set up properly.

If I want to use 2 phones, is there a way I can set one up to spoof its number so it looks like the other one?
So I can have for example a Vodacom phone and a CellC phone, and just use one number as my main number, then the other phone spoofs to look like the main number?
(for voice calls)

 

[Arthur]

Of course it's easy in software, but I doubt the networks' licensing agreements permit this. Still, maybe someone in the know can shed some light on this. Technically it's a few mouse clicks and a rattle of 10 keys.