When his cellphone starts playing the Britney Spears song Toxic, David Bauguss knows his girlfriend is calling.

When his boss calls, the phone plays the old Survivor rocker Eye of the Tiger. The opening bars of the James Bond theme means his dad is calling. Bauguss hopes to download a version of Men At Work's Who Can It Be Now? for those annoying callers whose numbers don't show up on his caller ID.

As he sits behind the desk of the US Cellular kiosk in Valley View Mall, Bauguss scrolls down his list of ringtones, which, simply put, are the sounds a cellphone makes when someone calls. In all, he has 20 separate ringtones, from snatches of hit songs to electronic chirps and beeps. The days of a simple electronic ring are passing.

Ringtones are what everybody wants, said Bauguss, an assistant area director for Cellular Express, which sells US Cellular's calling plans. If you have a high-end phone, you can download a song, chop it, put it in a flash drive and play it.

If phrases like ringtone, chop it and flash drive are as foreign to you as Sanskrit, you're probably not the target market for customized ringtones.

They're mainly for the younger market, said Bauguss. People in high school, college.

That's music to the ears of the recording industry, which for years has watched its younger audience be siphoned off by the easy availability of free music on the Internet. It turns out that many of the same young people who think nothing of downloading hours of free music will pay up to $3 for a few seconds of a song to put on their phone. According to two published reports, ringtones accounted for as much as $375 million in revenue last year in the United States. Worldwide, revenues exceeded $3 billion.

They are so popular, Billboard Magazine has added a weekly chart of the hottest ringtone songs. The magazine named 50 Cent's In Da Club Ringtone of the Year during its annual awards in December.

Some of the most popular ringtones today include Snoop Dogg's Drop It Like It's Hot, Ciara and Missy Elliott's 1, 2 Step and Usher and Alicia Keys' My Boo.

Whatever the hot song is, that's going to be the most popular ringtone, said Jermon Cobbs, a sales representative for One-Stop Cellular, which retails products for Ntelos, SunCom, T-Mobile and Cingular.

Many phones can only provide electronic-keyboard soundalikes - sometimes called polyphonic ringtones - of favorite songs, but more people are opting for expensive phones that can play actual MP3 samples of real songs. Called Master Tones and Real Music, they bring the highest prices for downloading.

Recording artists are quickly getting into the game. Kanye West, Ludacris and Q-Tip are among several hip-hop stars who have signed deals to provide voice or musical ringtones for cellphone entertainment companies that sell tones, games and screensavers. Madonna has her own ringtone shop on the Internet.

The Internet is a virtual shopping mall of ringtone providers, with Modtones, Xringer and Ringster among the most popular. Most ringtones can be delivered to a phone immediately if the owner knows the phone's carrier and model number.

I think it's kind of fun to have different rings for different people, said Jessica Holmstrom, 18, a Virginia Tech freshman from Richmond. Her ringtones include a Kenny Chesney song for her mother and the Cheers theme for her best friend.

It's better than just random noise.

Even though a definite cool factor goes with having hip songs rise from your cell, there's a practical side, too.

Since everybody has a cellphone, you don't want to have the same ring as everybody else, said Tech senior Michael Ho. He was relaxing on a couch inside Squires Student Center, surrounded by other students armed with laptop computers and cellphones. It was a scene where a ringing cellphone could have sent a dozen people rifling through bookbags and purses to see if it was their phone.

Ho recently added polyphonic versions of Maroon 5's hit This Love and an Isley Brothers song to his ringtone list. That way, he can recognize his phone immediately if it rings in a crowded lounge.

The practicality of it is that you need something to distinguish yourself from everybody else," he said. "Everybody tries to get a different ring. You don't want to sound like everybody else.Billboard's top ringtones

for its Feb. 5 issue

(SETH, you can check some ringtone audio at modtones.com)

For Extra story 1.31

HOT NUMBERSBillboard's top ringtones from its Feb. 5 issue1. Drop It Like It's Hot, Snoop Dogg featuring Pharrell Williams

2. 1, 2 Step, Ciara Featuring Missy Elliott

3. Get Back, Ludacris

4. My Boo, Usher And Alicia Keys

5. Shorty Wanna Ride, Young Buck

6. Boulevard Of Broken Dreams, Green Day

7. New York, Ja Rule Featuring Fat Joe & Jadakiss

8. What U Gon' Do, Lil Jon & The East Side Boyz Featuring Lil Scrappy

9. Over And Over, Nelly Featuring Tim McGraw

10. Super Mario Brothers Theme, Koji Kondo\