Spotify's music subscription service is a great way to discover and share music, and with its mobile app and a Premium account, you can take its huge library of songs with you anywhere.
But every once in a while you'll encounter a track that isn't on Spotify, but you know you have it in your personal collection. On a Spotify Playlist like the one shown here, you'll see these tracks as grayed out and unplayable.
The situation isn't hopeless. With a little extra work, you can meld your music collection into the Spotify app, and leave the iPhone's stock music app behind.
To see a video version of this tutorial, head over to CNET How To.