Disabling Operator ("0") option for Exchange Mailbox

Default Option when creating UM Dial Plan  in Exchange 2010 is to have "Operator extension" is set to 0 (UM Dial Plans/Properties/Settings)

If you need to disable operator for certain mailboxes (users) here is the list of steps to follow:

1. On Exchange: create the new UM Dial Plan - make sure that "Operator extension" is set to empty (UM Dial Plans/Properties/Settings) - name the new UM Plan to something like "4-Digit No Operator".
2. Set "Subscriber Access" extension on the new UM Plan: (UM Dial Plans/Properties/Subscriber Access).
3. Create new Hunt Groups for every IP Gateway (UM IP Gateways tab), make sure to use the new UM Dial Plan and Pilot Identifier set in step 2 for subscriber access.
4. Disable Unified Messaging for the user/Enable Unified Messaging specifying new UM Dial Plan during enabling process.  That concludes Exchange portion of configuration.
5. On PBX: configure PBX to call new subscriber access (set in the step #2) for the user/users that should have operator option disabled.
6. On IP Gateway: make sure that subscriber access extension (set in step #2) is in the scope of extension that target Exchange UM.