It was only a matter of time. Everyone else has been getting on the slider bandwagon, so now Sony Ericsson has done it too - the only mystery is why it's taken them so long? Available in either black or white, the W850i retains the orange detailing of all the Walkman range, though it's getting progressively more subtle - this time it's limited to a single flashing bar beneath the screen and backlighting for the music controls.

This slider though certainly doesn't see itself in competition with the rash of skinny flip and slide models that have emerged in the wake of Motoroloa's RAZR - it's a touch chunky at 21mm thick and sits heavily in the pocket, though it feels exceptionally robust. The Walkman brand has helped Sony Ericsson carve out its own music maker mobile niche, so maybe it's still biding its time on muscling into the skinny side of things.

The onboard main 2-megapixel camera may appear more like standard issue now that Sony Ericsson has moved up to 3.2-megapixels with the K800i, but it's still better than most. And its 3G functionality really opens up this model for fast downloads of music and video plus streaming of content and fast as you like full web browsing.

All in all then, the W850i has some pretty good things going for it. The phone's focus, not surprisingly, is on music, and you can use it as an MP3 player without the need to open the slider. The music controls are right up there on top, but fortunately they also double as navigation keys, so you can find your way around the menus and camera controls without the need to open the slide.

There's quick access to the Walkman music player via that illuminated orange strip at the top of the control pad - press it no matter what menu you're in and you'll go straight to your music.

Lights, camera, phone

There's a setting which gets the orange strip to light up in time with any music you play (though it struggled a bit when we tested it with Bach!) so you can take your own pocket disco with you anywhere. And if you want to make your disco public, while the loudspeaker could hardly be described as muscular, it's not bad for a phone speaker, and perfectly adequate for demoing your latest fave tracks to your mates.

The music player has the latest Walkman Player 2.0 software of course, which includes shuffle and loop functions, plus Sony Ericsson's new TrackID service. It works in a similar way to existing music ID service Shazam - you hold it next to a speaker (or activate it while listening to your phone's built-in FM radio), it takes a sample and a few seconds later gives you the name of the track and the artist.

In theory it's a bit cheaper than using Shazam though, since it doesn't require a phone call (it enquires via a data call), and you only get charged for the data transmitted, which isn't much.

The TrackID system uses the frankly awesome Gracenote database, which includes very nearly everything that's ever been recorded and officially released, so there's a very good chance it will be able to identify what you're hearing. It certainly picked up on everything we tried it with, from trance act Moonchild to northern soul also-rans Spanky Wilson and obscure indie rockers the Wolfhounds.