It's rude when you're with other people you should be paying attention to. I literally yell at my friends; it only helps a little bit.
Standing in line...eh. It's a bit annoying for everyone else in line, but as long as they can still function (unlike the woman RoD supposedly yelled at), it's not much more annoying than when people have a full-blown conversation with the person next to them.
I feel self-conscious when I use the phone though. I was at lunch by myself the other day, and one of my best friends calls me to talk about her breakup -- I was very aware of the poor guy next to me at the counter the whole time.
