You can just go to the User > Telephony > Supervisor Settings and check the box for Outgoing Call Bar - this would stop the user from making any external calls except those that use dial emergency features.

To restrict to 911 and local calling area, create a new ARS table with entries such as
1707261XXXX / Dial 3K1 / 1707261N / Line Group
1707265XXXX / Dial 3K1 / 1707265N / Line Group
etc.