I have one, but unlike the obvious crowd, I'm very respectful. If in a public place, its either offline, or on vibrate (at which point I leave the facility or go to the restroom to talk if I must (rare. I'm not one to use a phone often).
My phone is far more than a phone. Its a palm-pilot (smart phone) which keeps (among my nursing school
stuff such as drug lists and the Davis Drug Guide (palm edition) and care-plan notes, my very sechedule etc.)
Its also the only phone I have (I am 'wire free').
About the rudest I can think of, is some jerk using the phone in a theater during a movie. That happened, and my normally gentle self became somewhat indignant (the guy received 3 calls, then MADE one, he was two rows back, 1 seat over). I got up, explained that if he didn't turn the (expletive deleted) phone off, I was going to shove it so far up his (behind) he would have to open his mouth to extend the antenna.
I was riding the cycle that day, and can be rather imposing when I get my dander up. Suffice it to say that the individual got up, left the facility (didn't make it back in for bout 20 mins -(whats the point in seeing the movie?) and I got more than a few 'thumbs-up').
I'm not a violent person, but that kind of behavior really grinds me. if you are THAT important that you must have a conversation on your phone in a crowded movie theater, then please just buy out the theater for a showing, and watch it yourself (celebrity style)