What you're really asking... in my opinion... is... am I that irresponsible to text, check emails and chat on a cell while trying to drive on the interstate and jeopardize my life and the lives of others? Am I that rude to do all of this while I have someone trying to talk to me? No... not me.
I give my attention to my driving first. I don't use a cell phone at all while driving. I can't pay attention decently, if I have a phone in my hand.
Even if I am not driving, I would never be so rude to another person with me by talking on a phone while trying to hold a real time conversation with someone.
This is supposed to be "common sense" and good manners.