==Quickly adjust the volume on the iPhone==
By default, the two volume keys found on the left side of iPhone adjust the ringer volume from the smartphone.
During a telephone conversation, the same couple of buttons changes the power of the speaker or hands-free mode, as the active mode.
Finally, in applications using sound effects or sounds (like the iPod or games) the same time the slider changes the volume, without affecting the volume control on the ringer.
Last refinement, connecting the headset to the iPhone automatically switches the iPod playing, while conversely you put music automatically paused by unplugging.