@Thunderchild,
I was not referring to legitimate uses like you and Nigel describe. I was referring to the idiots on American highways - the ones who have a cell phone permanently on their ear, are eating or smoking, and trying to drive at the same time. When I am following one of those people and see their head keep ducking down to look at something on the seat, I get really nervous. There should be a simple way to warn the person they are about to tailend.
John