While using the first two features are rather straightforward, and require you to use a Wi-Fi connection, listening to music from the game works a little differently. You'll need to play up to a certain point in the game to be able to listen to the music that includes the likes of A-ha's 'Take On Me' and David Bowie's 'The Man Who Sold the World', and they can only be played within the app.
In order to make the most of it, you'll need to be on a Wi-Fi network to which your PS3, PS4, or Xbox One is connected. Yes, there is no support for the Xbox 360 or PC. A crying shame considering how well the game is selling on Steam.
The Metal Gear Solid V: The Phantom Pain companion app is available for Android and iOS. Smartphones and tablets on Android require to be on Android 4.2 or later. And if you're on iOS, you'll need an iPhone 5S or above and iOS 8.0 or later.