BlackBerry introduced a new subscription music service Thursday, tying music streaming to social networking through its popular BlackBerry Messenger (BBM).

For an additional US$4.99 per month, BBM users can stream and store 50 songs per month. Once they reach the cap, they are able to swap up to 25 songs on the list for new ones -- or they can build-up their music libraries by connecting to other BBM Music users and gaining access to their 50 songs.

The service, powered by cloud music vendor Omnifone Ltd. , is available on a limited trial basis in the U.S., Canada and the U.K.

Why this matters
RIM's BBM service is already highly addictive amongst its 45 million-strong user base, and the handset maker is hoping to entice more people to join by adding a music service that gets more valuable the more "social" you get. It's another step the company is making to build up its apps and draw in the consumer market, which has largely opted for iPhones and Android devices instead. (See Apple Borrows From Competitors for iOS 5 and BlackBerry: The Mullet of Mobility.)

The problem with RIM's $5 service, however, is the growing number of other music services that are both free and unlimited. Spotify just launched its free online music service in the U.S., for example. A premium mobile version costs $10 per month, but downloads are unlimited. (See Spotify Hits US 3G Networks.)

Music is one mobile app that could pit handset makers against the wireless operators as well. Both MetroPCS Inc. (NYSE: PCS) and Leap Wireless International Inc. (Nasdaq: LEAP) offer their own unlimited music download services, built into the prices of their highest-tier data plans. (See MetroPCS Taps Rhapsody for Unlimited Music and Leap Hopes Music Will Muve It Nationwide.)

For more
Here's more on how music is shaping up on mobile.

— Sarah Reedy, Senior Reporter, Light Reading Mobile