I just found this question while searching for something related to push notification.
You can achieve this by listening to the push notification and start playing sound in your application when you receive the push notification.
1) for iOS7 and higher, you can get a push notification, even the user does not open the application using this method
- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler;
2) . AVAudioSession, , . documentation - , . , , , ..