If you are familiar with Nortel Telephony systems you may have used something called Express Messaging.
This feature allows you to dial a pre-defined number (from any phone) and type in a persons extension number to acces and leave them a voicemail message.
This feature was widely used at the organisation I work for.
We now have a new telephony system installed based on a Nortel CS1k connecting to Exchange 2007 for Voicemail using Unified Messaging.
There did not seem to be any way to replicate the Express Messaging feature on the CS1K so I looked into doing something using Exchange.
The obvious candidate was using an Auto Attendant
Found a really helpful Blog from Geoff Clark here
http://blogs.technet.com/gclark/archive/2009/03/30/exchange-2007-um-transfer-to-voicemail.aspx
And it turned out that with 2 simple Exchange Powershell commands;
New-UMAutoAttendant -Name <> -SpeechEnabled $False -Status Enabled -UMDialPlan <> -PilotIdentifierList <>
Set-UMAutoAttendant -Identity <> -AllowExtensions $False -CallSomeoneEnabled $False -SendVoiceMsgEnabled $True -NameLookupEnabled $False
The required feature could be replicated.