Microsoft has quietly filed for a trademark that may allude to a unified app store for both Zunes and Windows Mobile phones. The filing for the name "OneApp" would cover not just an app download store for cellphones and media players but would also address a developer kit for the same platform. Among the apps suggested possible through the service would include games, media playback, messaging and mobile payments.

The trademark is unlikely to apply just to Windows Mobile given the existence of Windows Marketplace for Mobile as a separate store. Instead, the name and description suggest the possibility of OneApp referring to developers writing a single program that can work on more than one platform.

Microsoft has both publicly and privately dropped hints that it wants to integrate Zune with Windows Mobile and that elements of the media player could arrive on the smartphone OS. Zune devices, particularly the Zune HD, are based on the same basic Windows CE foundation as Windows Mobile and so could theoretically run programs built on common code.

The development of a single software store is potentially crucial for Microsoft, whose media players have been hurt by the absence of touchscreens and significant third-party apps like the iPod touch while its smartphones have had an app base but have lacked a strong media component like the iPhone. [via istartedsomething]