The problem right now is that even if I had a couple of million dollars lying around, I STILL couldn't reliably get a piece of hardware certified for the cellular network. I would have to set up a company, spend untold amounts of money bribing^Wwooing cellular company executives for a couple years, and, maybe, just maybe, I could get my phone through the certification process.
The technical aspects of certification are the easy part.
The problem is that the cellular companies fully understand that when it happens their power goes to zero because they suddenly become a dumb pipe that everybody just wants to ignore.
That's why this will take legislation.
The sheer technical difficulty is what makes this kind of thing impractical.
The network does validate that a SIM card is a real SIM card, but you can put a "real SIM card" in anything.
The M1 Macbook Air is 5 years old now, has an active development, lots of community funding and attention, yet is still missing basic functionality like external monitors and video decoding. Because it's just a mammoth task to support modern hardware. Unless you have a whole paid team on it you've got no hope.
Because the number of non-Google and non-Apple phones is a rounding error.
And why is that? Because, except for the incumbents, it is almost impossible to certify a phone.
We could have nice sub-$100 phones (remove camera, etc.) if people could get them certified. But they can't; so we don't.