Spotify released applications that allow users to listen to songs from the Sweden-based company's library using Apple or Android mobile devices.
Previously the service was available only from laptop or desktop computers, unless users paid for a subscription.
"Today we're giving people the best free music experience in the history of the smartphone and the tablet," said Spotify chief executive Daniel Ek.
Spotify also expanded its reach to 20 new markets, bringing to 55 the number of countries in which the service is available.
Ek also used the New York press event to announce that the catalogue of rockers Led Zeppelin would soon be available on Spotify, a move expected to attract more users to the service.
The company boasts 24 million active users, with more than six million of those paying for a premium ad-free service costing $10 a month.
Free versions of Spotify are supported by ads in a model similar to that of California-based Pandora.
"Spotify's move to offer a mobile listening experience to users who do not subscribe signifies the company's hope to use the free mobile experience to get another six million people to first try it out for free and then eventually splurge for the on-demand subscription," said Forrester analyst James McQuivey.
The free service lets people listen to songs generated in play lists and does not allow selection of specific tunes on-demand.
"Spotify's move this week is not only good product marketing in the present, it's necessary positioning for that future, in which Spotify itself will likely have to become a feature in somebody else's product, or disappear."
Created in 2006 by two Swedes, Spotify, while labeled the world's most popular streaming music service, has yet to make a profit, unlike its US rival Pandora.
In 2012, the company said it lost €58.7 million, on sales of €434.7 million ($594 million).
McQuivey said that Spotify is out for users' time and attention in a market where titans such as Apple, Amazon, Google, and Microsoft each offer a "cloud music experience."