By Jim Reed
Newsbeat technology reporter
The W902 phone will offer around 3 million tracks for download
Sony Ericsson will soon start selling Walkman phones with unlimited music downloads included in the price of the handset.
The mobile phone maker is the latest to announce a subscription service, joining its bigger rival Nokia and the pay-TV operator BSkyB.
Users will be able to download millions of tracks while they are signed up to a standard mobile contract and keep up to 300 songs after the deal ends.
Play Now Plus
Sony Ericsson's service, called Play Now Plus, is expected to launch in the UK at the start of January 2009 to coincide with the 30th anniversary of the original Walkman portable music player.
Users will be able to buy a special edition W902 phone with access to a library of around 3 million tracks.
Phone networks are expected to subsidise the cost of the handset, making it free on some contracts but with a reduced number of minutes and texts.
Tracks can be copied directly to the phone over a mobile network using a format called eAAC+, which is designed to keep download times down to around 8 seconds per track over a 3G connection.
Music will be copy-protected which means it cannot be transferred to another portable music device like an iPod.
It can only be played on the owner's computer and personal mobile phone handset.
When the contract is up, users can extend the life of their music library for an undisclosed weekly fee or keep up to 300 "most-played" tracks in MP3 format which can be copied to another device.
Music subscription hopes
Over the last year, major record labels like EMI and Universal have slowly come round to the idea of mobile music subscriptions.
Nokia is also launching a deal that allows unlimited music downloads
By offering unlimited access to tracks, they hope to stop people using file-sharing networks like BitTorrent and Limewire.
Rob Lewis, the boss of Omnifone which has developed the technology used by Sony Ericsson, said: "The 15-30 age group has historically been involved in illegal file-sharing because they are more interested in discovering new music.
"The key is to move those people over to legitimate services."
The Sony Ericsson launch will come months after its rival Nokia starts selling phones bundled with its 'Comes with Music' service.
Like Play Now Plus, it lets users download unlimited amounts of music from all the major labels.
Instead of paying per track, customers are expected to pay around £70 extra on top of the original phone price, although some networks might subsidise the cost of a handset.
Unlike Sony Ericsson, Nokia hasn't yet agreed deals with network operators.
As it stands, users will have to download music to their computer before copying it over to a phone instead of downloading tracks directly over the 3G phone network