Sony Ericsson has announced plans to launch a mobile (and online) music store in the second quarter of 2008 in a bid to counter moves by Nokia (NYSE: NOK)—and to a lesser extent Motorola (NYSE: MOT)—into the mobile services market. It has signed up the big four labels: Sony (NYSE: SNE) BMG, Universal Music Group, EMI and Warner Music Group. “The situation today is that we have offers on the table of five million music tracks, as a first step, from all the majors, as well as local and independent labels,” Sony Ericsson’s Martin Blomkvist, head of content acquisition and management, told the Wall Street Journal. He links it to the PlayNow service, which is in 29 countries and has 100 revenue-sharing agreements in place, but until now only offered music from Sony.

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The “open platform” mantra was raised, and the formats will be MP3 and Windows Media so the store will work with non-Sony Ericsson (NSDQ: ERIC) handsets. It appears that Sony Ericsson is taking a different route than Nokia, talking about partnering with operators and sharing revenue with them, from “the music downloads, as well as sales of computer games, ringtones and phone wallpapers.” And, of course, there’s a bunch of new Walkman phones. That leaves Samsung and LG (SEO: 066570) as the main handset manufacturers who have yet to announce music store plans—of course, their over-all business is different from mobile-focused Nokia and Motorola and Sony Ericsson, which has a label as a parent.