Contrary to statements published in various third party integration documents, it is possible to include mail-enabled contacts in the Directory Search functionality of a Dial Plan or an Auto Attendant in Unified Messaging.  Although the following configuration steps can provide this functionality, you should exercise caution when enabling outbound dialing from Unified Messaging.

• Calls to the Subscriber Access (SA) line of a UM Dial Plan are considered unauthenticated until the caller enters a valid PIN.  Outbound dialing restrictions set on the Dial Plan affect unauthenticated SA callers.
• Calls to the Subscriber Access (SA) line of a UM Dial Plan are considered authenticated only after the caller enters a valid PIN.  Outbound dialing restrictions set on the associated UM Mailbox Policy affect authenticated SA callers.
• Calls to a UM Auto Attendant (AA) are considered unauthenticated as the caller is never prompted to enter a PIN.  Outbound dialing restrictions set on the Auto Attendant affect unauthenticated AA callers.

For example, if you allow unauthenticated callers to search/dial mail-enabled contacts from an Auto Attendant menu, you may incur national or international long distance charges unless proper dialing restrictions are enforced. 

Please see the following TechNet article for more information:

Managing Outdialing in Unified Messaging ( http://technet.microsoft.com/en-us/library/bb232135.aspx )

Configuration Steps

1. Launch the Exchange Management Console and drill down to Recipient Configuration in the navigation pane on the left
2. Click on Mail Contact, then select New Mail Contact from the actions pane on the right
3. Create a new Mail Contact called UMContact with an email alias of UMContact and an external email address (i.e. umcontact@nwtraders.com)
4. Open the properties of the UMContact object and enter a telephone number in the Business field of the Address and Phone tab
5. Next, open the properties of your UM Dial Plan (or UM Auto Attendant), click on the Features tab, and allow callers to contact Anyone in the Default Global Address List
6. Open the Exchange Management Shell, then enter the command:  set-contact “UMContact” –createdtmfmap $true
7. Using AD Sites and Services, replicate all of your domain controllers in the Active Directory site where your UM servers reside
8. On each UM server associated with the UM Dial Plan, open a command prompt and navigate to \Program Files\Microsoft\Exchange Server\BIN
9. From the command prompt, run:  galgrammargenerator.exe –g –o .\generateGAL.log to manually generate the grammar file for the Global Address List
10. Open the generateGAL.log file using Notepad and verify that the UMContact object was processed successfully
11. Using a telephone, call the Outlook Voice Access/Subscriber Line for the UM Dial Plan, and log in as a UM Enabled user
12. From the main menu, say ‘Directory’ then search for the UMContact object (it should find the contact object and prompt you for confirmation)
13. Next, say ‘Call the Office’, then place a call to the Business phone number of the UMContact object

-- Dave