Yo, the mobile app that used to just say Yo and still claims "It's that simple" as a tagline, has been adding features like hashtags and the ability to include links with content attachments. Beta List founder Marc Köhlbrugge has discovered that they also have a hidden file that "specifies the MP3 file they should play on your device" when a Yo is sent. This ability opens up possibilities such as music messaging which could lead to music selling as well. But if that doesn't pan out, you'll still be able to use any of the growing number of music-related...

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