In this hypothetical scheme (described above), a child complaining about anonymous abusive messages is ignored by the school. School's not responsible, because the child's phone is set up improperly. If phone were in order, phone would not receive anonymous messages.

A child receiving a traceable abusive message is quickly resolved, and presumably this kind of abuse is rare, for obvious reasons.

Everyone is happy. The school's happy because, under this scheme, they have virtually no work to do in connection with online harassment. The police are happy because fewer harassment cases are being opened (this is true only if most kids set their phone as instructed by the school). Kids are slightly less miserable because online bullying has been made more difficult to pull off.

Finally, sticklers like the parent are happy because they can continue to set up their phone "wrong" and receive anonymous abuse. Which the school won't look into and will presumably pass off to the police.