Cellular Carriers Search For Piece Of Music Biz; Where Is The Revenue?; Ring tone downloads are hot sellers, but full-song business may be trickier.(INTERNET & TECHNOLOGY)

Byline: REINHARDT KRAUSE

Besides house keys and wallets, mobile phones may be the most common thing people carry around these days.

Wireless companies see that as a big selling point as they try to tap the digital portable music craze. They figure people would rather put all their music on their cell phone than carry an additional music device.

But as Samsung, Nokia and others rush to build cell phones that play music, wireless service providers are struggling with the shift. They want to embrace digital music features, but they also want to make money in the process. It's unclear how that would happen.

At the heart of the issue is how cellular users get songs onto their phones.

They could download songs directly from their personal computers -- just as they do with Apple Computer's iPod.

But that could cut Cingular Wireless, Verizon Wireless and other cellular carriers out of the loop.

Or users might download songs onto phones via their cellular service. But it's not clear if subscribers are comfortable doing that. And downloading speeds are often too slow to be practical.

"The jury is still out on …