Just be reasonable Ok, how about this for a compromise; Normally cell phones are not permitted during the flight, but if the flight is behind schedule, then the crew can provide a 15 minute period were phones will be allowed. That way travelers can inform whom they need to that they are going to be late.
This allows you to lets say change an 11:00 meeting to 1:00 because of the flight delay or to inform someone meeting you at the airport to get there later so that they don't have to wait around for you.
These types of calls are reasonable but still allow most of the flight to be quiet for those whom prefer to read, sleep, etc.
I know it is difficult to regulate common courtesy, but allowing people to make a quick call is also reasonable.