From Reuters (link):
Peng Shan, a spirited 21-year-old Beijing design student, changes her cellphone’s ringback tones as often as people change clothes, part of a growing fad that’s delivering piles of cash to China’s mobile carriers.
“They reflect my feelings,” she said cheerfully in a phone interview. “I choose a lively pop song when I’m delighted, and a soothing ballad when I’m frustrated.”
Catering to Chinese subscribers’ increasing desire for personal expression, ringback tones — the sound a caller hears in the seconds they wait for another person to answer — are turning a marketing gimmick into big business.