Hi Karmon,
The cell phone issue is a tricky one as you have explained. The issue has to be handled on a local basis, meaning what ever policy your school sets and then what you will accept in your class as the instructor. I think you have developed a very reasonable policy based upon your student population.
When starting a new class I discuss with the students the rules that will be a part of the class structure so there won't be any misunderstanding. As you well know each phase there are those students that violate the rules and I deal with them individually.
I will say that it seems to be of less a problem as we move along due to the fact that people are learning more about what the proper use of cell phones are and respect for others. Something we have to keep on top of along with everything else.
Gary