Assistance for a beginner please

Could someone point me in the right directon? We are running * with a Digium card providing 4xBRI ports. We also have a DID range provided by our telco so that we have numbers 555-50xx. All calls coming to 555-5090 are being automatically forwarded from Auckland in New Zealand to our Sydney office. All of these, and other international calls arrive here without Caller ID. I would like to “set” the Caller ID for calls coming in from 555-5090 as “NZ” for example.

I would appreciate any clues as to how this might be done. Thanks for reading the post.