Please note: this headsets with iphone1, 3G no volume on addition and subtraction. Other functions are normal.

Line control operation Guide:

Press the pause/play, press twice to jump to the next song, press three times to return to the previous song. In 3GS/iphone4 long press to bring up the voice control function

With remote control and microphone Apple earphone uses popular Apple headphones and ear plugs on the cable of the control unit, including a microphone and three buttons.

Use the convenient remote control what can be done: 

Adjusting the volume press the + and-buttons.
By pressing the Center button to control music and video playback, including play/pause and next/previous track