I would imagine that with a Phone OS, it would no doubt have a payment system. Then the govt could automatically get a VAT cut with every transaction. Plus a payment profile. THAT is is why they want a local phone OS.
Always follow the money.
Of course, given the logistics involved (not the technology), I am not sure a nation-state can go beyond the theming and regionalisation as in one of the parent posts - just too much politics will get in the ways.