For short sounds or when the MP3 does not play well on the suggested code you can always use:
SystemSoundID soundID;
NSURL *url = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/sound.mp3", [[NSBundle mainBundle] resourcePath]]];
AudioServicesCreateSystemSoundID((CFURLRef)url, &soundID);
AudioServicesPlaySystemSound (soundID);
Don't forget to add:
#import