I agree that students should pay attention in class and not do anything that may distract them or others from the subject matter at hand; that includes using cell phones.
However, is it really a teachers place to punish them for it? Teachers who take students' phones away, or even worse, throw it against the wall/stomp on it/etc. (look it up on Youtube, it happens) seem to be overexerting their authority. To me, that says violation of your right to property.
If I were a teacher, I would let my students do whatever they want, as long as they don't do anything completely obnoxious (i.e. talking to each other across the room, making loud noises, etc.). If they want to sit in their chair and quietly use their phone or laptop, then why should I care? Chances are, them doing so will mean that they might miss important material and not do as well on assignments and tests, but I leave that up to them. Why should I care if they use their phone to text or check Instagram during class, so long as they do it quietly and keep it to themselves? After all, they're the ones paying to take the course (well, referring to U.S. colleges at least) not the other way around. If they choose to distract themselves and fail the class then that's their loss, they're the ones paying tuition anyway.
Then again that's just me.