These are the people swerving all over the road because all of their attention is on talking on their cell phones. It is amazing how many almost wrecks I have seen because of this. These people are swerving worse than someone who has had too much to drink.
This is definitely an annoying and dangerous habit, Jack. Good that you brought it up.
If I'm not mistaken, some places are thinking of banning (or maybe have banned) cell phone talking while driving.
I can understand just giving a status report ("hey, I'm late, be there in half an hour") but not long chatty conversations.