Research In Motion (Nasdaq: RIMM) is going business casual. The mobile device maker best known for serving corporate email has debuted a music subscription service called BlackBerry Messenger Music, or BBM Music, in which users pay $4.99 a month to share songs over instant messaging.

Each subscriber gets up to 50 tracks to add to his or her profile, from a library of more than 10 million via license agreements with Warner Music (NYSE: WMG), EMI, Universal, and Sony's music division. BlackBerry hopes to tap into the growing convergence between social media and entertainment .

"The service is compelling because it's social," RIM's vice president for BBM Platform & Integrated Services, Alistair Mitchell, told Bloomberg in an interview. "It's about that conversation around music that's the centerpiece of it."

And that's different? Color me skeptical. Not only did Apple (Nasdaq: AAPL) try and fail with a social music service called Ping, but rival music service Spotify also allows for simple track sharing and has its own mobile apps. Pandora Media (NYSE: P) rose to fame in part because of how it helps users experiment with playlists.

Let's also not forget Sirius XM (Nasdaq: SIRI). Smartphones may be aggregating on-the-go audio entertainment for many of us, but the satellite radio supplier still serves more than 20 million subscribers. I'm guessing that more than a handful of those listeners use Sirius' BlackBerry app to get their fix.

In this sense, BBM Music is an add-on -- and a limited one at that. Don't expect it to add color to RIM's otherwise bleak profit picture. Do you agree? Disagree? Please vote in the poll below, and leave a comment to tell us your thoughts about the service. You can also add Research In Motion to your watchlist for up-to-date analysis on the stock as soon as it's published.

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