• A UM dial plan has been created. For detailed steps, see Create a UM Dial Plan.
  
• A UM mailbox policy has been created. For detailed steps, see Create a UM Mailbox Policy.
  
• The user's mailbox has been UM-enabled. For detailed steps, see Enable a User for Unified Messaging.
  

You need to be assigned permissions before you can perform this procedure. To see what permissions you need, see the "UM mailboxes" entry in the Unified Messaging Permissions topic.

1. In the console tree, navigate to Recipient Configuration > Mailbox.
   
2. In the result pane, select the mailbox for which you want to add a new extension number.
   
3. In the action pane, under the mailbox name, click Properties.
   
4. In <Mailbox User> Properties, click the E-Mail Addresses tab.
   
5. Select the appropriate Exchange Unified Messaging proxy address (EUM address), and then click Edit. In UM Address (Extension), in the Address/Extension box, type the new extension number.
   
6. In the Dial plan (Phone context) box, click Browse to locate a new dial plan for the user.
   
7. Click Apply, and then click OK.
   

You need to be assigned permissions before you can perform this procedure. To see what permissions you need, see the "UM mailboxes" entry in the Unified Messaging Permissions topic.

This example changes the extension number to 22222 for Tony Smith, a UM-enabled user.

Note:
You must determine the position of the EUM address that you want to modify. To determine the position of the EUM address, use the $mbx.EmailAddresses command. The first proxy address in the list will be 0.

$mbx = Get-Mailbox tony.smith
$mbx.EmailAddresses.Item(0) ="eum:22222;phone-context=MyDialPlan.contoso.com"
$mbx | Set-Mailbox

For more information about syntax and parameters, see Set-Mailbox or Get-Mailbox.

After you modify the extension, you may also want to:

• Add an Extension Number for a UM-Enabled User
  
• Remove an Extension Number for a UM-Enabled User