What you need to do it open the Exchange Administrator (admin.exe) in raw mode with the /r switch. You then will want to delete the raw object for the orphaned Unity server and the Unity folder. If the customer wants to introduce Unity again they will need to make sure that the 'voice-mail-user-ID' property is set to 0 on all of the subscribers too.
Keith
Keith Chambers
Diagnostic Engineer
Voice Network Team, San Jose
Cisco Systems, Inc.