Spotify is apparently interested in expanding its mobile music services by offering users free (ad-supported) on-demand access to streaming music. The company’s current offer lets users stream unlimited music on their smartphones and tablets from a catalog of over 20 million tracks for $10 per month, or stream Pandora-like radio with ads for free. According to The Wall Street Journal, Spotify has inked deals with Sony Music Entertainment, Universal Music Group and Warner Music Group for an enhancement to its ad-based services that will allow on-demand music streaming. Spotify already has a similar free access offer for desktop and laptop users, although it doesn’t include unlimited music streaming. Mobile users who sign up for the free option will also have some