Don't you think it's interesting though, how you can carry on a conversation with people in the car, and it's fine, but on the phone, it seems to be more distracting. I wonder why.
Maybe it's just my passengers that are good, but typically, with people in the car, if they see a situation that might require more concentration on driving, like bad weather or whatever, they'll keep quiet because they know you have to pay more attention. People on the phone obviously aren't able to do that because they don't know what's going on.
Also, as a driver, if I shut up for a couple minutes to give more attention to my driving, the others in the car will see why and won't question it. People on the phone tend to try to keep the conversation going.