12 Ultrasonic Ringtones For Your Nearly-Silent Listening Pleasure
5:00AM July 13, 2009 | Jack Loftus
The kiddies have been using ultrasonic ringtones to secretly take calls/texts in class since 2006, but if you’re an adult who can still hear these frequencies then by all means head over to Lifehacker for some of your own [Lifehacker]
