I remember watching a programme about dog whistles; whenever someone blew into one, a dog would rush forth but humans would not be able to hear it. I then learned that it was because our eardrums aren't quite as good as those of dogs.
And then again, such quality can be limited to youngsters. Shortly before school started, a company produced a ringtone, 'Mosquito', that was configured so that only students could hear it. When school started for me, it turned out that the ringtone had become so popular that many techers knew what it was, What may seem as a disappointment may be that two of our teachers were able to hear it loud and clear; in fact, one, our marine biology teacher (I stopped her course to pursue Spanish last week), demonstrated it to other teachers. It turned out that she had been a musician and had kept her ears healthy that way. On the other side of the spectrum, though, our gym teacher — the same one that assigned the mechanical babies — was led into the room as Dan, one of the ringtone owners, played a sample for her. She couldn't hear it, so she made us turn around and raise our hands if we heard it. When most of us did, she accused us of lying and stalked out. The ringtone has proved so successful that I also heard shopkeepers intend to use the sound to drive hoodlums away.
Even so, I haven't seen the need to text in class or otherwise use a mobile phone during those hours. My stepbrother was ecstatic to receive one the Christmas before last, and ever since then he's wanted the best and the most expensive out of it; he's used that thing for more uses than it's been designed for, from what I can tell. I'm the exact opposite; since mine was not a flip phone and it kept turning on when I brushed against a wall, and I never had any cell phone numbers to keep anyway (only that of Tom, whom I haven't communicated with much since I started working), I stopped using it after four months of being forced to have it on me and gave it to one of my father's labour contractors. This Christmas, though, I may be getting one of Cingular's 'go' phones and, when I receive my licence, AAA services. The main concern in my family was being stranded on a dirt road, which I saw as the only use for a cell phone if ever there was one.
And there's also the possible meet-ups. Lily did mention calling Frostweaver via mobile once....