There are plenty of times when you DON'T want that Top-40-hit ringtone going off in a room full of people. Oh, you can set your phone on "vibrate," but that buzz is still audible enough to attract attention (and maybe make you flash on the "dildo in the luggage" scene from FIGHT CLUB).
What's the solution? How about a ringtone that only YOU can hear?
Ultrasonic Ringtones offers just that: ring tones in the 8KHz-22KHz audio range, i.e. right up at the top end of your hearing range. The idea of ringtones in the dog-whistle end of the spectrum was first championed by schoolkids, who wanted to take cell calls under their teachers' noses.
The site lets you "test-drive" each frequency before downloading it, but also cautions that hearing it on your computer and actually using it on your phone are two different things. They also caution that anything over 12KHz will probably be inaudible to people over the age of 20. Still, the 8-12KHz range tones might be right up your alley — they'll still cut through all kinds of ambient noise, and you won't mistake anyone else's phone ringing for your own.