Wired covers the emergence of ringback tones for mobile phones outside of Korea.

"Ring-back tones are not to be confused with the ring tones that sound off when you receive a call. Rather, ring-back tones are snippets of music that are played to callers while they wait for the phone to be answered, instead of the usual ringing we now hear."

"Brent Wyman, senior vice president of commerce, sales and marketing at technology provider Cellus USA, reported that on average a third of all Korean subscribers already use the company's My Caller service, which was introduced in April 2002. The Yankee Group puts ring-back revenues in Korea at well over $100 million for 2003."

I'm a bit more skeptical with ringback tones as they produce a much smaller audience. anecdotal evidence from my personal teenage "early adopting product testing group" shows little buzz. But the service is simple and cheap to establish and can produce some extra revenue from existing infrastructure. So we surely see it productive in near future. Meanwhile I'll think about mine ....