Millions of people use Twitter to talk about their favorite music, and now Twitter is using that data to build its own version of the Billboard charts with its new (and free) iPhone and web app called #music.

“[The app] uses Twitter activity, including Tweets and engagement, to detect and surface the most popular tracks and emerging artists,” Twitter wrote in a blog post announcing the new service.

Rather than developing licensing arrangements with record labels, Twitter instead opted to partner with subscription music services Spotify and Rdio.  Both services charge a monthly fee to access their libraries of millions of songs. Music plays through the iPhone and web app directly without having to load another application. Without a music subscription the app will instead play iTunes previews that will link to the iTunes music store where the songs can be purchased. Twitter says they will be working on adding more services to the platform in the future.

Tracks are listed in four different categories.  “Popular” lists the most talked about music in the Twitterverse at any given moment.  The “Emerging” category finds rising stars that haven’t yet hit the top of the charts but are generating a lot of discussion on the social network. “Suggested” recommends tracks based on what Twitter knows about the user to help discover new music. And the “Now Playing” category pulls in what other Twitter music listeners have indicated they are listening to. Thankfully the app doesn’t automatically share what is being listened to unless the user generates a tweet.

Twitter says an Android version will be coming soon. Watch our video review above to see it in action!

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