Quote Originally Posted by kexodusc
Although personally I've never understood why talking on a phone distracts a driver so much more than talking to a passenger in the car...
Think of it this way, a passenger sitting next to the driver in the car sees the same changing road conditions that the driver sees, and must react to. If something comes up that requires the driver's immediate attention causing a pause in the conversation, the passenger will see it too, and should understand without explanation.

Someone on the other end of a phone conversation is unaware of that. Too many of us allow phone calls to dominate over any other circumstanses we find ourselves in. We lack a socially accepted convention that allows us to say I'm too busy right now to pay attention to your phone call - don't take it personally.