Streaming music service Rdio, formerly available only on a pricing plan, just announced that it's launching a free streaming service today. To sign up, you simply need an email address or Facebook account. Rdio's plan for converting users to paying customers is a new ad-free version with a meter that tracks the number of free monthly plays available. CEO Drew Larner told Fast Company that the allotment is "dynamic," meaning that a user that only regularly streams a few tracks won't be prompted to become a paying user, while one that consistently maxes out free plays could be faced with the need to pay. Larner isn't exactly clear where this point is, but Rdio's introduction of a freemium service, combined with increased visibility through Facebook's new ticker, should be effective for bringing new users onto the service.