Music subscription service Rdio first gained attentionwhen Kazaa founders originally announced it as their latest foray into the digital music space. The service got official a couple months later with a Web service and apps for Android and iOS devices. Today, Rdio added one mobile OS to the mix: Windows Phone 7.
Much like, Rdio is designed in deference to the operating system. As such, it, too, has a very Zune-like interface--I'm beginning to sense a theme here. As far as music apps are concerned, Rdio competes much more directly with the Zune Pass service. However, it may have a leg up in pricing: Rdio is $9.99 per month, whereas Zune Pass is still $14.99. The latter includes 10 MP3 download-to-own tracks each month, though, which does add value.
Other than that difference, Rdio and Zune Pass operate in much the same way. You can listen to all the music you want from a multimillion-song catalog, and download tracks and playlists directly to your device for offline playback. Both also offer social elements that serve to recommend new music. Zune Pass still might have a bit of an edge, though: it's native to Windows and offers a larger catalog as of press time.