I totally agree, but today this is almost impossible. Many years ago for a company to save money they used a technology share with their employees. Here is what it entails:
Issues that arose for technology sharing:
Many companies still use this plan today. Therefore, it would be difficult to restrict phone, tablets or even PCs in the work environment.
However, if a company doesn't use technology sharing I'd have to say it is best to not allow an employee to use his phone during business hours unless it is a total family emergency. Nowadays the school will call you on your mobile device if there is a problem with your child. Personal calls should be restricted to non business hours only.