"About 4 years ago, a US visitor here (UK) was shocked to see that nearly everyone had mobile phones"
The US is far from homogenious. A decade ago I was flying all over the US and cel phone usage was about the same as Toronto, my home base at the time. The sight of the odd person holding a cel and talking into it was not uncommon.
So like, I fly to San Fransisco and again, this is 1997, get off the plane and walk through the concourse. I see a guy talking, apparantly to himself with a blank stare like he was here but not really here if you know what I mean.
Then I notice they're all doing it. Holy shit! Zombies!
Turns out they were just early adopters of cel phone headsets and they'd achieved near ubiquity at least at SFO. I'd never seeen these before.
The crab cocktail and sourdough bread soothed my jangled nerves in the land of blue suited zombies that afternoon.