Music listeners who sign up for the service will be given unlimited access to its library of more than 15 million tunes for six months. After that, the standard limits on a free subscription will kick in--10 hours of listening per month and during that time, no one song can be listened to more than five times.

The service also has . For $4.99, there are no time limits and no advertising. For $9.99, you have the added benefit of being able to download the songs in your online playlists to a mobile device and play them offline.

The free part of the service is by far the most popular. In Europe, for example, where Spotify has some 50 million subscribers, subscribe to one of the paid plans.

Spotify's CEO Daniel Ek leaked the news of the move to TechCrunch writer Alexia Tsotsis at the Facebook F8 developer's conference.

will take some time, Ek told Tsotsis, but immediate access to the offer can be obtained by registering for Spotify through Facebook.