A history of the cell phone ringtone.

Many recent hip-hop songs make terrific ringtones because they already sound like ringtones. The polyphonic and master-tone versions of “Goodies,” by Ciara, for example, are nearly identical. Ringtones, it turns out, are inherently pop: musical expression distilled to one urgent, representative hook. As ringtones become part of our environment, they could push pop music toward new levels of concision, repetition, and catchiness.