If I were Steve Jobs, the video to the right would scare me senseless. It shows a Google Android phone running a Spotify app that appears to succeed in porting the full Spotify experience — still not available to most Americans — to a mobile phone.

We’re not alone in thinking that the Sweden-based Spotify is the best desktop music application on the planet, even though its legitimate use is currently restricted to Finland, France, Norway, Sweden, Spain and the UK. On the mobile phone, it becomes a serious threat to the iTunes/iPod ecosystem. Who wants to bother with buying songs track-by-track, when you can work with a customizable library containing millions of tracks, for free (with the occasional ad) or a monthly fee?

We’ve called Spotify on the iPhone the “end game” for mobile music. This Google Android version of the app, demonstrated last night at the Google I/O Developer Conference in San Francisco, boasts a crucial feature we predicted Spotify would add: the caching of playlists for offline listening, which lets you play your music (or playlists other people have created) without a WiFi or 3G connection.

The video to the right shows a user selecting which playlists to cache, listening to them, adding a song to a mobile playlist via laptop, as well as a Jobs-style “one last thing” at the end of the presentation depicting the app’s ability to play any song or album on-demand.

If Apple doesn’t allow a full-fledged version of this app into its App Store, music fans with Spotify access could switch to Android, if the message board on Spotify’s blog is any indication.

The Spotify desktop application runs on a P2P streaming architecture; as you use it to listen, you’re also uploading song data for other users to stream. This architecture doesn’t work as well in a mobile setting, with reduced bandwidth and processor speed, so if Spotify mobile apps become more popular than their desktop counterparts, the system could come under strain. Other than that, it’s hard to see how this Android app won’t be a runaway success — where it’s available, anyway.

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