RIM has announced that the BBM Music app will soon be available for download in the US, Canada, and Australia, a few months after it launched on a limited trial basis. Like Spotify and Rdio, both of which are available for BlackBerry, it's a socially connected music service — with somewhat of a twist. A Premium subscription allows users to build a library from the BBM Music catalog that's available to be streamed (and stored for offline listening), but unfortunately you're limited to 50 songs and can only swap out 25 of those songs each month. However, you can add to your song collection by connecting with other BBM Music Premium users to gain access to their libraries (10 BBM friends, 500 more songs). In addition, its $4.99 monthly fee is still cheaper than other services that offer unlimited streaming and offline caching — for example, Spotify requires a $10 monthly subscription for mobile listening.