This falls into approximately the same zone as Self-explanatory sentences...
When some gadget or word or habit has become universal, you'll never hear an official statement saying "Everyone now has X" but you can generally pick up an indication from popular culture.
In the last few days I've picked up such implicit indications that the cell phone has become totally and absolutely universal.
1. A local radio ad features two women talking on the phone. Beth is telling Tina about some kind of new exercise place, and Tina keeps trying to interrupt her. Finally Tina gets a word in, and says "But Beth, I'm already there." This would have made no sense at all in the days when a phone was a device permanently fixed to the wall; when Beth called Tina, she would know exactly where Tina was. The idea of a surprising location would have been incomprehensible.
2. At the downtown bus station, a black man approached two white women. I thought he was going to ask for a cigarette, but instead he said "Got a phone?" Since black men have absolute authority, one of the women gave him a phone. He called one of his homies and rapped for a while, then handed the phone back. Again this request would have been incomprehensible 30 years ago. A phone simply wasn't something you carried in your pocket, available for borrowing.