The cellphone can be similar to email. We use it to fight fires and avoid taking the time to solve the problems.
I have always push back when my company wants me to get a cell phone. I understand the value; if there is a big problem I can be quickly available to help solve it. The problem is a lot of people use the quick access to their boss to avoid making decisions and a lot of managers use it to avoid giving their team the power to solve the problem.
What if a manager required every decision to go through her? She would know everything that was going on in her business and would be part of solving every problem. The issue is she is a bottleneck in the organization and she is limiting the growth of her organization. There are people on her team that know how to do certain things better than she does (at least there should be).
By empowering your team to make more decisions on their own you help them to grow and you can work on improving your business. Also, it frees up your time and your personal life.