I agree with all the comments you have made about cell phone abuses. I agree the conversation can usually wait until you're out of the store/bathroom/car/etc. There is always, "I'll call you back."
But then, my dh deployed. He only calls me once a week. He was a truck driver before that, and I could call him all the time, which I did. He'd call me, we talked all the time. Now I can only talk to him for a few minutes once a week. So when he calls, I'm answering, and I don't care where I am. I've answered in restaurants, bathroom stalls, (once, and it was really awkward), when I'm volunteering at the zoo, stores, in meetings, etc. I haven't heard my dh's voice for a week, and I miss him terribly. So sometimes, there is more to it than just "what kind of tomato sauce should I get."