A Microsoft Lync Server 2010 Standard Client Access License (CAL) user tries to use the basic call control functionality by using a Lync certified USB audio device, such as a headset or a speakerphone. In this situation, the user cannot use the following functionalities:
Answer and end calls.
Hold and resume calls.
Mute and unmute calls.
Note This issue does not occur when the same user performs the call control actions from the Lync 2010 client instead of the USB audio device.
To resolve this issue, install the following cumulative update:
2571543 Description of the cumulative update package for Lync 2010: July 2011
Note The following functionalities remain limited after this update is applied:
The device switcher menu is disabled.
The dial-pad functionality is disabled.
The other functionalities are limited according to the user's license.
For more information about the pricing and licensing options for Microsoft Lync 2010, visit the following Microsoft website: