PCB, from the research listed in the link I posted, it isn't the act of holding the cell phone that distracts drivers, it's the conversation. Some people should not have passengers in the car with them, as some conversations with passengers can distract the driver as well, hence the law in Massachusetts that prohibits teen drivers from having passengers in the car with them other than their parent or legal guardian.

One of the German rules of the road I cited gives the polizei the lattitude to determine if the driver is being distracted or not, allowing them to concentrate on truly distracted driving rather than making them pull over everyone talking on a cell phone/drinking coffee/etc while driving.