When we first heard about Rdio going to a free, no-ads service, the immediate question was how it was going to work. Today, we get clarification. Essentially, it’s metered, which is what we had heard before. The details? In short, you don’t get to go mobile, and there’s a meter on your use.

Free access users will see a customized meter at the top of their profile page indicating how much free music they have each month. At any time, they can choose to upgrade to one of Rdio’s flexible subscription plans for unlimited music streams and Rdio’s mobile apps.

If you decide that you want to go mobile, you’ll need to step up to one of Rdio’s other plans. That includes the $4.99 “Web” plan that lets you play Rdio via the Web or a desktop app, or you can go up to $9.99 and pick up mobile, including iPad, Sonos and Roku. Need a family plan? $17.99 gets you 2, or $22.99 gets 3 subscriptions.

It’s not a huge move, but it’s interesting. After seeing Spotify go “free” for 6 months on Facebook, and MOG deciding to go ad-supported on the whole, it’s not a terribly surprising move from Rdio. Still not sure which one you want to use? We have a great round-up here of a few services, and of course a listing of the best alternatives.