Sci-fi that turned real

There must be an early 80’s science fiction story where kids of an advanced civilization carry a pocket sized super computer to school and schools need to remind kids to keep their computers (which they call telephones for some weird reason) in a back-bag and on silent.

I would have enjoyed that story as a kid but wouldn’t have believed it will happen on my lifetime

Piece of paper on a Finnish school door that says in Finnish: “keep your phones on silent and in your backbag, please”