@sashh
Schools need to have a clear and consistent policy.
Yes! At my DS's school, there was a "school wide" policy of phones turned off and in bags during the school day. Fair enough. Rigorously enforced for Year 7s at the start of their school life!
But then you had some teachers who wanted their pupils to use their phones to take snapshots of the whiteboard, or to Google for researching etc during lessons. So that gave them very mixed messages.
They also put all homework on "show my homework" including worksheets etc., so if a teacher was absent and hadn't left work, the cover teacher would tell them to do homework, meaning they had to log in with their smartphones to see the homework and do the worksheets or links to the online quizzes etc.
More mixed messages.
And yes, some teachers encouraged them to listen to music whilst doing work as they thought the pupils are less disruptive when listening to music than they'd be just working in silence!
So many mixed messages. I think the real answer instead of banning them, is proper education as to the benefits and disadvantages and a very strict, coherent and consistently enforced set of rules as to when and where they are used. Outright bans never work, just look at drugs, smoking, underage sex, etc - teens regard rules are made to break, especially those they don't understand or which are illogical.