It is illegal for all drivers to use a handheld wireless communication device unless the vehicle is stopped

The answer is in a school zone.

It is illegal for all drivers to use a handheld wireless communication device in a school zone unless the vehicle is stopped.

The reason for this is that operating a handheld wireless communication device while the vehicle is in motion requires the driver to take his/her hand off the steering wheel. This can in turn result in loss of control of the vehicle. If this happens, it can put the lives of innocent students at stake.