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Spotify charges $10 a month for unlimited access to tracks on mobile devices, but a PC-based version is free in the U.S. with no caps on usage for now. Clicking on friends’ passive posts puts a program on one’s computer that plays back the song.

Freeing people from the hassle of actively sharing songs they like will help keep people engaged in their friends’ listening habits without effort, said Spotify’s chief content officer, Ken Parks. “Anything that brings the friction out of that is great for everybody,” he said.

Rhapsody, a competing $10-a-month unlimited mobile music service, announced it would allow Facebook users 30 days to try out their service, even on mobile devices. Competitor Rdio is giving users a free 7-day trial on mobile devices too.

“The more you help people discover music, the more social it is, the more they will be engaged,” said Rhapsody president Jon Irwin. “If they’re more engaged, then they’re more likely to subscribe.”

Facebook continues to add users and has 800 million globally so far. That has made it a huge director of traffic on the Web, and now its display advertising business is bigger than online news giant, Yahoo Inc., according to eMarketer.

That’s one reason news media companies are jumping on board.

Yahoo developed a way to let Facebook users know what stories their friends are reading after logging in. A running tally of stories friends have clicked on appears at the top of the page. The plan is to start the integration with the news section on the U.S. site and expand it into the sports, finance and entertainment sections next year.

The Washington Post launched an app called a Social Reader that creates unique front pages that pull from multiple sources based on what you and your friends are reading. Washington Post Co. CEO Donald Graham said the plan is to draw a big audience but not put advertising in the app for now.

“What do newspapers need right now? Great journalists and great technologists,” Mr. Graham said. “We have plenty of great journalists and they have the great technologists.”

AP Business Writer Michael Liedtke in San Francisco contributed to this report.