At first, I thought my technology manager was telling a joke when he told me about teens using high frequency ring tones on their cell phones, but turns out they're very popular. Students are using them, of course, to alert them when a text comes in during class. Seems that teens can hear sounds at higher decibels than we "old" people can.
Honestly, I was a bit skeptical until he showed me this website from Free Mosquito Ringtones. Go ahead, test it yourself. I recommend you get someone younger than you to sit with you just to prove it. If you want to know how each sound corresponds to age, see this page.
Yes, this is just another method to get around the rules of the school that govern the use of cell phones in class. I say it's still pretty cool though and I read that a student came up with the idea-way to use your noggin' kid-pretty cool stuff!