*UPDATE* - Looks like the mobile apps portion is still limited, bad wording on their post. @RdioHelp confirms mobile access still requires a Unlimited accnt. But they still offer a 7-day free trial.
While we could debate the streaming music services available these days, including BBM Music -- I'm personally fond of using Rdio. For a number of reasons really. They have a great selection of music, support multiple platforms and their mobile apps are great -- including their support for BlackBerry devices. Now, they've gone ahead and made things even better for those looking to get in on the services:
Some of the best things in life are free, and starting today, Rdio is one of them. New Rdio users in the US can take advantage of many of our popular features for free, including streaming full songs without hearing a single ad — a meter at the top of your profile will show you how much free music you have each month.
An email address or Facebook account is all you need to start listening for free, and no application downloads or credit cards are required. Just sign up at rdio.com or through one of our mobile apps to get started.
You can sign up using your Facebook account but they do offer the email sign up as well in case you don't have a Facebook account. Overall you can't really beat ad-free music which is available for streaming to your device. Give Rdio a shot, it's a really great service.