It was my job for a decade to try to keep tweens and teens safe online. Let me tell you what you already know: no law or technology can do it. There are no lengths kids won't go to to talk to friends without prying eyes. The harder you try to lock it down, the dodgier their solutions will be.

@mttaggart We did this with phones back in the day.

The school installed a fancy phone system (in the early 80s so no mobiles) with no outside dialling on most extensions.
We found a phone with outside access and diverted calls to it to an outside line. Then we just had to ring that extension from any other and we had an outside line to ring anywhere. Simples!
Kids will always find a way.

@mikecox @mttaggart I'd argue it's an important skill to nurture.

Like with your example - I'd hope that there were staff who were aware of the work-around and just let it go, since it doesn't hurt anything (well, maybe the school's phone bill 😂 ) and more importantly shows initiative.