Spotify is shifting its model to allow free, ad-supported streaming worldwide on mobile devices, after previously charging a premium for access on smartphones and tablets.

"We wanted to make something really great, something that fits into (users') lives," Spotify CEO and founder Daniel Elk said at a press conference in New York announcing the news.

The Spotify Free for Mobile service will let users access songs in a shuffle mode in a radio-style mode based on playlists or artists -- on smartphones, it doesn't let you select specific songs. Tablet users, though, will now have on-demand access for free. The company said Spotify Premium, priced in the U.S. at $9.99 monthly, "continues to offer the ultimate listening experience" with on-demand, ad-free access to music on multiple devices.

Elk, who noted that Spotify has returned $1 billion to the music industry, also announced an exclusive deal to add Led Zeppelin's Swan Song/Atlantic catalog to the service. In addition, he said Spotify is launching in 20 new markets today -- including Chile, Colombia, Czech Republic, Hungary, Peru, Slovakia and Uruguay -- for a total of 55 markets worldwide.

Stockholm, Sweden-based Spotify has more than 24 million users worldwide, with about 6 million paying subscribers. The company is facing a growing set of competitors including Apple -- which recently launched iTunes Radio -- as well as Google, Rdio and Pandora.

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