Apparently there's a sound which no "adult" can hear. Kids in the UK have been using it as a ringtone, so they can recieve calls in school and their teacher wont know.
It's based on the fact that your hearing degrades over time, although I can hear it and so can Cheryl (and technically we're too old) .. so i'm interested to see if you guys can too.
Click here to listen to a wav of the file. Then let us all know if you hear anything.