Facebook just became a better place for musicians to share their music, as the service has just launched a “Listen” button with prominent placement on musician pages.

It looked like Spotify was the service of choice when I first checked out this feature, but it appears that Facebook will automatically fire up the music service that you use the most. This is going to be a huge boon for services like Spotify and Rdio, which are already seeing a lift from Timeline and real-time listening links in Facebook Ticker.

Here’s what the Listen button looks like when you visit a prominent musician’s page on Facebook now:

When you hover over the Listen button you’re told that this feature, in my case, requires Spotify, and once clicked a modal pops up prompting you to launch the music service’s app:

This is the type of feature that makes Facebook the perfect place to browse for new artists, as when you see that your friend has liked a band that you haven’t heard of, you can immediately listen to some of their tracks.

This is exactly why a service like Spotify combined with Facebook is Apple’s worst nightmare. Not only does this give people more of a reason to stay on Facebook, it completely changes the way that people explore music. It’s also a feature that MySpace saw massive success with in its early days.