1. I've noticed this as a "dumb-phone" user who often forgets it at home. Walking around with your head up, you feel like you're amongst a bunch of half-asleep people. You can look right at somebody and they won't notice you. Lots of bumping into each other, not making way for somebody who needs to get by, things like that. Many people who are engrossed in their phones don't react to loud noises or other things happening that are out of the ordinary. It can be unsettling.

2. A few months ago I was sitting in a crowded urban park. I was people watching for a bit; no book, no phone. I saw some sort of surveillance/tracking operation unfold in plain site. A fit, ex-military looking guy in his mid 40s dressed to look like a tourist in a t-shirt and shorts took a seat. He would steal glances off to the side at a certain individual. He talked into his blue tooth ear piece, casually glanced around, and then he took off his blue baseball cap, put it in his backpack, and quickly replaced it with a red baseball cap. He later shot me a little grin, having seen me noticing him, even though I was discrete and over 30 meters away.
Over 100 people could have seen this unfold but I am sure none did because almost all of them were looking at phones.