This thread should not be dominated by discussions about spectrum regulation. It is about economics of operating mobile networks and service pricing.
Spectrum HAS TO BE regulated by International Agreement, end of story.
It is in the very first instance an issue about interference, especially between countries. The technical rules are set.
After that, it is about how many networks can be supported in the same geographical area using the same technologies or even different technologies without causing undue interference between them.
And that IS driven by how many services and users can be supported in total in a specific band
And THEN one can start arguing about how many competing operators will be able to economically operate in a band.
As SWA has pointed out already the average is about 3 operators with the minimum being 1, and the maximum being 7-8.
Now in our market, we have only a handful of operators operating in the same bands (2 dominant, plus 2 limping along).