UPDATE: Today (12/11) Spotify confirmed new mobile and tablet functionality, among other things. Users of the free software can now shuffle their playlists or any artist catalog on their phones, and non-paying tablet users can stream any song on demand as they could on a desktop. The company also announced it has launched in 20 new markets. And it’s signed up Led Zeppelin: The band’s first two albums are streaming now and the rest will be rolled out over the next few days.

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Earlier this week, Spotify rolled out some explanation of its royalty payments in an attempt to boost its reputation following high-profile naysaying from artists like Thom Yorke and Beck. Now comes word that after a year of negotiations with Sony, Universal, and Warner, the Swedish music-streaming company (currently valued at $4 billion) is expanding its free on-demand service to mobile devices.

Currently, Spotify’s free ad-supported on-demand streaming is offered only on its desktop software. According to reports by Wall Street Journal and AP, next week the company will announce functionality that lets users choose specific tunes on their mobile devices too, but not without limitations: The tracks will have to be added to a big-enough playlist and will only be shuffled, with audio ads. That playlist can only be played a number of times, but apparently such restrictions won’t be as strictly imposed on songs the user has already streamed. Via TechCrunch:

The reasoning may be that Spotify sees these subsequent plays of songs users have already shown interest in as less valuable than on-demand access to what they’ve never listened to before. Reserving infinite search-and-listen capabilities for premium customers ensures people don’t get the milk if they don’t buy the cow. When the free tier launches, these limits may not be especially easy to understand, our source says. That could confuse users, leading to poor user experiences where people think they should be able to listen to something but they can’t.

Or perhaps this will give non-paying users a taste of what they’d get for $10 per month and convince them to upgrade. The enhanced service is expected to be announced formally on Wednesday.