A Ring Tone Meant to Fall on Deaf Ears - New York Times

"In that old battle of the wills between young people and their keepers, the young have found a new weapon that could change the balance of power on the cellphone front: a ring tone that many adults cannot hear.

In settings where cell phone use is forbidden ? in class, for example ? it is perfect for signaling the arrival of a text message without being detected by an elder of the species."

I read about this in the New York Times (print edition) today

A ringtone most adults are unable to hear. The tone was first developed by Compound Security Systems as a tone that was meant to detour teens from congregating in areas such as outside shops and convenience stores. The tone was hacked and converted to a ringtone and now is used a way of sending txt msgs and phone calls in the classroom. The tone used in the ringtone was a close match the tone used by Compound Security Systems. The tone is now officially being sold by the Compound Security Systems on their website.
I can hear the ringtone, see for yourself if you are able to hear the tone here.