Agreed, back when I was in highschool, smartphones were relatively new, and even then the benefits were obvious in the form of being able to use them for music in any sort of study hall and for the calculator, and in university it quickly became very normal to see people taking a photo of things they thought would be especially noteworthy (which was very helpful because professors would often be going too fast to note it down). My highschool had the additional option of bringing and using a laptop in class, which I always used and found to be far more convenient.
I get that social media and texting are distractions in the classroom, but I really don't buy that a blanket ban is the solution. That's just draconian and brings to mind all the other arbitrary rules/limitations I had/have to deal with as a student which just built up resentment and encouraged malicious compliance rather than any respect of the school.
Also brings to mind the old joke about teachers telling kids to solve even complicated equations (without convenient numbers) by hand because "you won't always have a calculator at hand", and how wrong that turned out to be.
Edit: Come to think of it, it's interesting that social media sites haven't thought to do something about this as a PR move. They could sell beacons (specifically to schools) which if the phone detects, it notifies the teacher. Not being able to get away with sneaking a look at a phone would quickly reduce the issue of having to tell kids to put their phones away.