They’re shrill, synthetic and can last less than 20 seconds. But music fans can’t get enough of those jingling ringtones.

Want proof? Billboard magazine this week introduced the first Top 20 “Hot Ringtones” chart. It says a lot about what kind of listeners favor phone-friendly serenades and just how popular those tunes have become.

The inaugural top ringy-dingy choice goes to … drumroll … “My Boo” by Usher and Alicia Keys.

It inspired 97,000 purchases last week.

By contrast, the No. 1 legal song download of the week – U2’s “Vertigo” – drew 25,000 buyers.

Ringtones are outselling legit song downloads by more than 3 to 1, even though those nagging tones tend to cost almost twice as much ($1.99 versus a buck) and don’t give the listener the actual tune, only a rinky-dink imitation.

According to Billboard chart czar Geoff Mayfield, the magazine started tallying ringtone purchases because “it’s a very important new revenue stream for the industry.”

The mobile-music market adds up to roughly $300 million in the United States so far, according to Mayfield. Four million consumers are said to be “active” users, meaning they switch their Ringtone at least once a month. Tens of millions are “occasional” users – those who tend to stick with the same tone for a six month period. Internationally, the market for ringtones is $3.1 billion.

In contrast to games and other information services available on cell phones, “everyone has some kind of ringtone, and most people want to choose theirs,” according to Adam Zawel, a wireless analyst for the Yankee Group.

And Mayfield expects a second growth spurt when the industry rolls out its next innovation – “mastertones,” featuring the actual recording rather than today’s sonic mimic.

Europe and Japan are ahead on mastertone technology, but some American cell phones allow their owners to download songs directly from their players, letting them make their own ringtones.

Mayfield says another reason Billboard decided to highlight ringtones is that “they offer an indication of just how vital music remains in the minds of consumers.”

After all, by purchasing a ringtone you’re showing your identification with an artist or song. The service gives fans a quick, if strident, way of announcing their musical taste to the world. A purchase also means that the listener wants to hear a given song over and over again.

According to Michael Gartenberg, a technology analyst for Jupiter Research, this trend measures the increasing “personalization of the cell phone. It has become such a part of peoples’ lives that the No. 1 thing they want with them when they go out is a cell phone. And the No. 1 thing they want to do when they’re outside is make a phone call.”

The data for Billboard’s Hot Ringtones chart come from a wide variety of distributors and wireless carriers – enough, according to the magazine, to cover more than 90 percent of the American market.

The most popular ringtones in the U.S. now come overwhelmingly from the world of hip-hop, which indicates the youthful market for singing cell phones.

Believe it not, the No. 13 Top Ringtone is Vanilla Ice’s reviled old “Ice Ice Baby.”

The only non-hip-hop song in the Top Five is the theme from John Carpenter’s movie “Halloween,” no doubt in deference to the season. The selection says something telling about ringtone choices:

They’re impulsive and fleeting.

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(c) 2004, New York Daily News.

Visit the Daily News online at http://www.nydailynews.com/

Distributed by Knight Ridder/Tribune Information Services.

AP-NY-11-05-04 1005EST