Click on the extension you wish to change and select the PSTN/Billing Settings section.
To change the caller ID, select the number you wish to use instead from the PSTN caller ID dropdown box. You can choose any of the numbers on your account.
If you would prefer to withhold your number for all calls, tick the Withhold CLI box.
Click Save to enable the change.
If you want to change the outbound CLI for all the extensions on your account, scroll down to the Change Master CLI section on the extensions page. Select the phone number you wish to use from the dropdown box and click Save.
Please note that any extensions that as set to present a withheld number will not be affected by this change. If you want to update these also, tick the Override withheld setting box.