Maybe they lack common sense,but the no cell phone rule was put in place for a good reason. If a player is allowed to use one for this case where do you draw the line. There are a vast number of injuries and players getting dinged up where a family member might be concerned about the players well being.
Apparently there are plenty of cell phones on the sidelines anyway, so if some one wants to reassure a relative that their brains have not been scrambled they can ask the trainer to call the relative and then put it on speaker phone