For portable CD player or MP3 player * For headphones and speakers headset couples one divides two line ,Stereo 3.5 audio 1 divides into 2 lines,for iPhone4G 3G/3GS1.Audio / Video Interface2.For portable CD player or MP3 player3.For headphones and speakers headset couples one divides two line ,Stereo 3.5 audio 1 divides into 2 lines,for iPhone4G 3G/3GS