If you are using Windows and the volume adjusts itself when you are making and receiving calls, you need to make a simple change to stop the volume from automatically changing.
This is caused by a new feature introduced in Windows 7 which can be disabled using following simple steps:
1. Open "Sound" applet from Control Panel or right-click on Speaker icon present in the system tray and select "Playback devices" or "Recording devices" or "Sounds" option.
2. Now go to "Communications" tab and check the option "Do nothing" and Apply it.
Your volume will no longer be changed automatically.