The Rebirth of the Ringtone
In the early cell phone days, the ringtone was king. It mattered what tone you used and the better phones were distinguished from the lamer phones by their ability to transcend the tinny tones of MIDI. Your ringtone was a statement of who you were, and so people paid to make sure their identities were accurately represented in song.
Then, the ringtone started to go away. I can't peg exactly when it happened, but nearly everyone I know (which I recognize is a small subset of humanity) switched to vibrate. Particularly as texting began to explode in the middle of the decade, it no longer made sense to have a phone constantly dinging every time someone sent you an LOL.
I rarely hear a phone ring these days. Hell, I'm lucky if I catch a stray beep. Only those without much experience in the wireless world continue to derive pleasure from hearing "Achy Breaky Heart" every time an acquaintance calls. A phone on vibrate gives you a slight informational advantage over the people around you, but at the cost of your public identification with a kind of music. Somehow, putting your phone on vibrate seemed politely self-interested, not just plain sneaky.
But I think audio is coming back as a way of communicating with our devices. If everyone starts talking to their phones, I at least get to switch back on my ringer and play the Ying Yang Twins as loud as I want.