Sony Ericcson has announced its plans for its unlimited mobile music service. PlayNow Plus will launch with mobile operator Telenor in Sweden by the end of the year. A special edition of the W902 Walkman phone will be the first participating handset. The service will be available globally next year.

According to Reuters, the service will cost 99 Swedish crowns (US $15.24) a month. Subscribers can download an unlimited number of tracks to the handset or to a PC, using the PlayNow Plus Desktop. The handset will sync with the PC using broadband and 3G/HSDPA connectivity.

All four majors and many independents (none were singled out by name) are said to be on board.

There are differences between PlayNow Plus and Nokia's upcoming Comes With Music service. PlayNow Plus will allow users to keep 300 songs in a DRM-free after the term of the subscription has expired. This press release says subscribers can keep their "most-played" music tracks. My question is, Why do you have to wait until the subscription expires to get those MP3s?

Both have DRM. PlayNow Plus uses eAAC Plus format with highly compressed files for faster transmission. Comes With Music boasts it will allow users to keep all downloaded songs, but the tracks will be wrapped in Microsoft's WMA DRM. Both services allow for unlimited downloading during the service term.

PlayNow will allow for a la carte track purchases through its PlayNow Arena, the mobile music store that was re-launched last month. At the time of the re-launch, tracks were priced at 9 Swedish kronor (US $1.40) apiece.

PlayNow goes a few steps further with some social networking aspects, music news and charts. I'm curious to see exactly how Sony will incorporate the services of Gracenote, which it acquired earlier this year.

Another difference will be evident right out of the box. PlayNow Plus-enabled handsets will come bundled with up to 1,000 pre-loaded tracks. I don't care much for the song selection of pre-loaded devices, but other people might.

On paper, PlayNow Plus looks like the better deal. During the term of the subscription, both services are fairly similar. But PlayNow Plus handsets come with tracks, and the value of the MP3 tracks kept at the conclusion of the subscription probably has a retail value in excess of the cost of the plan. And although EMI will eventually get on board with Nokia's Comes With Music, it has already licensed its catalog to Sony Ericcson.

That's on paper. On paper, many services and devices look great but end up being hampered by poor user experience. The Zune has long looked good on paper but still lags behind the iPod and SanDisk players. Even the MusicGremlin looked good on paper. The devil is always in the details. And it's in the timing. The product needs to be timed to match the public's readiness for this type of product. And it's in the product's ability to fit with consumers' expectations. That's the iPod factor. People love iPods. Will they fit a second music player into their lives?