I do think there needs to be a USO for mobile coverage.
There was discussions on digitalspy about wifi calling, people were praising it in high numbers. But I tried to point out to them, if mobile coverage was proper in their area then there would be no need for wifi calling, it doesnt solve the ultimate problem which is lack of mobile signal coverage.
So whilst I have never had signal issues aside from at the coast, I do know issues exist, and for a modern USO, there definitely needs to be an obligation for the mobile carriers to have blanket coverage regardless of cost, it doesnt need to be 3g/4g 2g is adequate for voice and sms. That would surely need to be in place before a consideration to remove the copper voice obligations.
In my area, I get 4 bars on 4g in my bedroom, never mind outside and can push circa 70mbit download and 30mbit upload. 5 bars on 2g pretty much all the time.
When I was last in cromer, I couldnt sleep so watched some twitch streams using 4G probably about 100m away from the seafront.