You can listen to music using iPhone's Music App through RunKeeper. Just bring up the RunKeeper app, then select the middle blue tab that says "Add Music." You can choose a playlist or shuffle all music.
In these screenshots the user has selected their "Country" playlist and so the middle blue tab displays the word "Country."
You can also play music from some of your favorite music apps like Spotify or Pandora. Apple allows some 3rd party music apps to run in the background, so you can also use them simultaneously with RunKeeper.
Just bring up your third party music app first, select your music, then bring up RunKeeper and get tracking!
To control music while tracking, you can swipe up your iPhone Control Center or double tap your home button and navigate to your music app!
Third party music apps can simultaneously play with RunKeeper. Just tap on the Music Note icon along the top menu bar in RunKeeper, and you will have the option to select your preferred music player.
After you select the music player, you can decide if you want to use that music player "Always" or "Just Once" with the RunKeeper app.
While tracking you can bring down your music controls just by swiping down from the top of your screen!
Troubleshooting Tip: On iOS if you are using the in-app music player to control music from your iOS Music App and the music does not start when you start your activity, try reinstalling the app! Just make sure all activities are synced to RunKeeper.com first!
If you find playing a third-party app's music along with tracking is crashing the app, make sure to close any additional apps not in use!