Play a music when Calling app is running - iPhone

In my app, user have the option to call to other people in the contact book. Launch the calling app is easy, but what I want to know is whether we can play a short mu开发者_如何学Csic file when the calling is happening, so user can send their friends a nice music by calling them directly.

If we can play a music in a background, I also want to know if we can know when their friends catch the call instead of just playing the music file randomly in 10-15 seconds

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This isn't possible within the current SDK. Two things will prevent it.

1. Once a call is initiated the music playing in the background is stopped by iOS.
2. The voice/audio of a call cannot be altered by an application (to overlay music etc.)