effective_caller_id_number=${outbound_caller_id_number}
effective_caller_id_number=1234567890
Thanks @royce3, that wouldn't work for multi-tenant though would it, where you wanted to set the default CID to a specific number. You can do it as @DigitalDaz suggests via the dial plan manager though.
No, he was just suggesting changing the dial plan which would carry across should you transfer Fusion / FreeSwitch to new hardware or upgrade the system