mosquito ringtone

I was looking at google's listing on the top searched items. One of their lists included the "mosquito ringtone" as number one.

I found it really odd. As it turns out there's a site www.freemosquitoringtones.org that claims to have a ringtone that has a very high pitch so as to be inaudible to adults.

Then I remembered something I saw on television a few months ago. This became an issue as school children were thought to have begun to use it in school so as to avoid detection from their teachers.

Anybody know if this is true?