The mbrace system provides different services, e.g.:
• automatic and manual emergency call
• Roadside Assistance call
• MB Info call

To adjust the volume during an mbrace call, proceed as follows:
Press the W or X button on the multifunction steering wheel.
or
Use the volume controller of the audio system.

You can find further information and a description of all available features under "Owners Online" at http://www.mbusa.com