If you've been following the kids-hear-higher-sounds story, this is interesting. Anecdotally, my five-year-old boy's ears and my 28-year-old ones both had our threshold between 20k and 21k--so, I guess, I'm ready to teach school, 'cause I'll definitely hear a 15k ringtone. I'll have a headache from hell, though. Remind me not to frequent those Mosquito stores.