Originally Posted by lurkette

I think cell phone conversations are more distracting than "in person" conversations because your attention is not on your physical environment - it's split. If you're having a conversation with a person in the passenger seat, you're both in the car, on the road, and your consciousness (while distracted by a conversation) is still present in your situation. A conversation over the phone kind of produces that same "absence" that you get when you space out for a while and notice that you're five miles down the road and haven't really been aware of your surroundings for a while.