You wanted screenshots, and now, we have them. I got these off of ZU, who got these from the Greek version of the Spirit Tracks website.

Link and the pipes
Link discovers Zelda.
Link plays Pipes.

My speculation are that you pretty much swipe it from Zelda, whom you catch playing them. The last one shows Link playing the pipes, and somewhat how to play them. Hm…. I’m guessing you blow into the microphone and hit the color needed to play. (I think that was mentioned in the last news post.) Also, the URL of these images calls it a pan flute….

Source: Zelda Universe.