Lost time from cell phone use is a serious management problem, especially among hourly workers. From a strictly analytic viewpoint, An hourly worker's value to the company is based on how much work they accomplish in a given time period and are compensated based on that time. Anything that is not specifically for the benefit of the company during that time is an expense directly effecting the bottom line.
Management on the other hand is generally salaried and is a task based paradigm. They are compensated to perform specific functions within a specific time frame. It is often the case that management will work beyond normal business hours without additional compensation, so their time is not so stringently managed as an hourly employee who would receive additional pay and possibly overtime for working late.
From a company standpoint, the impact of personal cell phone use (or Facebook, net surfing, reading graphic novels, crocheting, or any other non-work activity) during company hours is much more detrimental among the hourly staff that those collecting a salary, although those collecting a salary should know better (of course, many abuse the privilege).