Employers can be held liable for accidents caused by their employees while driving and conducting work-related conversations on cell phones.  Under the doctrine of vicarious responsibility, employers may be held legally accountable for the negligent acts of employees committed in the course of their employment.

Employers also may be found negligent if they fail to put in place a policy for the safe use of cell phones.  In response, many companies have established cell phone policies.  Some allow employees to conduct business over the phone as long as they pull over to the side of the road or into a parking lot.  Others have banned the use of wireless devices altogether in a work vehicle.

There is an excellent "sample" of an employer's cell phone policy here at about.com.