Many large enterprises have multiple voice policies assigned across their user base, you may find that you need to change a large number of users from one voice policy to another, carrying out this maintenance in the Lync Server 2010 Control Panel will prove lengthy as you can only change one user at a time, below is a helpful Lync Server Management Shell command that will allow you to return all the users on a specific Voice Policy and them change them to a different one.
Get-CsUser -Filter {VoicePolicy -eq “<policyname>”} | Grant-CsVoicePolicy -PolicyName “<policyname>”
