The MB Pro 1 and the MB Pro 2 allow the direction of their volume controls to be reversed, to accommodate users who wish the wear the headset on the other side and want the volume controls to match.
When the headset is on, but not in use (i.e. no active call or music reproduction), press in and hold the volume switch for two seconds. The headset should then beep, and after releasing the switch, the voice prompt "Swap volume keys" should be heard in the headset.
Should voice prompting be disabled on the MB Pro, a second 'beep' will be heard instead of the prompt.
If you are using the MB Pro 2, then swapping the direction of the volume controls will also result in swapping the left-right audio distribution for stereo reproduction.