Exchange 2007 supports three codecs for Unified Messaging voice messages. I knew that you could choose which codec Exchange uses at the dial plan level, but until recently, I didn’t know that you could change this setting for individual users. The key is to use the CallAnsweringAudioCodec switch with the Set-UMMailbox command, like this:
Get-UMMailbox “paul” -CallAnsweringAudioCodec gsm
Of course, you can do lots of more interesting things with this cmdlet by using filters or other means to apply this setting to a group of users… say, your Entourage users, who can’t listen to UM voice mails recorded with the default WMA codec.
Technorati Tags: Exchange 2007, Unified Communications, Unified Messaging
Paul's Down-Home Page 
As I’m sure most people will figure out, the syntax is actually
Set-UMMailbox “paul” -CallAnsweringAudioCodec gsm