To add a local area code to all numbers dialed over a trunk:
- Login to the system administration
- Navigate to 'Settings -> Servers'
- Check that 'Area Code' is set (e.g. 818)
- Navigate to 'Trunks'
- Edit preferred trunk
- Set 'Local Area Code' = 'Yes'
- Click on 'Save'
- Now, if you dial '450-1675' , the system will add '818' in front and dial '818-450-1675'