Scenario: I am on my way to point A, or I have to wait above ground for a metro and I have a few minutes. I call a family member or a friend to pass the time. We talk for a few minutes and then I rush off of the phone because I am on my way to my destination.
Or:
I am on my way to point A, and someone else is on her way to point B. She calls me, and rather than let the call go to voice mail, I pick up the phone and we both talk until someone has to get off of the phone.
Or:

Someone is on his way somewhere and he calls me. He talks until he has to go and jumps off of the phone. I don't get to say what I wanted to say, and neither does he, I suppose.
Or:
I am on a date or out with a friend and he or she gets a phone call. He or she picks up the phone; perhaps he or she doesn't talk for a long time, but it nevertheless interrupts whatever is going on. I have done the same thing, but I usually say "excuse me, I should take this." Some people don't. Or there's the missed call with the voice mail beeping and the "excuse me, but I have to check this and call the person back" (and interrupt whatever is going on).
And I pick up a phone call, rather than ignore it to get even.
This is not a revelation, but mobile phones completely change how I (and everyone else) interact with other people.
And most times, it sucks.
**I know that I am not guilty of talking too loud on public transportation, out on the street or in a restaurant.