If those people are having a moment, and not to be dismissed out of hand because in their moment they happen to be staring at their phone, it can be a lost opportunity.
Recently, I've observed that you're more likely to meet someone, and end up in a long conversation, close to the point where either you, or they, show up. So, you could strike up a conversation with someone after sitting next to them for 30 minutes, each doing your own thing... but it's been my experience that when you show up, or when they show up, there's more of an incidental openness that can be exploited with a "hello" (or whatever suits the occasion).
Absolutely and I am mindful of people not having their personal space or privacy invaded in public. This dynamic changes in a social setting however where the expectation is to socialize or be friendly to others.
Recently, I've observed that you're more likely to meet someone, and end up in a long conversation, close to the point where either you, or they, show up. So, you could strike up a conversation with someone after sitting next to them for 30 minutes, each doing your own thing... but it's been my experience that when you show up, or when they show up, there's more of an incidental openness that can be exploited with a "hello" (or whatever suits the occasion).