By Jennifer Saba and Mia Shanley NEW YORK (Reuters) – Online music-streaming service Spotify on Wednesday launched a free music service for smart phones and tablets as it tries to hook a fast-growing group of users keen to stream tunes on their mobile devices. Spotify offers free music on desktop computers with advertising but customers previously had to pay for on-demand connection on their mobile devices. The more music you play, the more likely you will pay, said Spotify founder and CEO Daniel Ek during a press conference at Spotifys offices in New York. Ek also announced Spotify launched in 20 new markets for a total of 55 markets worldwide.