[Brockenstein]

>would those couples have engaged each other in meaningful conversation (meaningful to them) had cellphones not existed?

certainly some would

>Or does the presence of cellphones reveal that a large number of people were never particularly interested in engaging meaningfully with others but would only feign interest when the alibi of the cellphone isn't available?

I think that people are addicted or at least oblivious at how attached to their phones they are. And they see plenty of other people engaging in the same behavior, which makes it a social norm and validates that behavior. Everyone does it, so it's OK.

Although I can't help but chuckle, because the same sorts of people who wanted to look down on me back in the day for spending hours in front of a computer, building a website, learning how to program, or playing games, are glued to their phones nearly every second they can manage to find. When it came time to practice the sort of etiquette that they preached, they failed miserably.