If you have FXO PSTN trunks, then this functionality is provisioned on by your FXO Service Provider. Caller ID is not sent from the UC320 to the PSTN over FXO, but rather the telco sends based upon your FXO circuit.
If you have SIP trunks, then you simply configure the pilot number for the trunk and that will be sent to your SIP provider. Again, the telecom provider can override what you send for caller ID and set what they have provisioned.
This can be done on the Inbound Calls Page of the GUI. Select the SIP Provider tab. Simply create a new route for an inbound call and enter the DID and select the target for that route. Click use the number for outbound calls. Now when that target makes an outbound call on the SIP trunk the DID associated with the route is used as the outbound Calling Party Number.
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