No problem, we have seen a lot customer requests that would like numbers in Auckland and Wellington on the same device, as we know easy to do technically but the rules constrains us commercially ....

DDi's are generally a PABX term for mapping numbers to EXTN's what you would have would be a number block assigned from a carrier where they will have a number range and will be giving you a block of numbers from this range , up to the Carrier on what they do with this but it's the Carrier owners responsibilities to make sure they comply with the rules, same way if the police were tracing a phone number they would go to the Carrier as the owner of the number not you as the wholesale provider.

When you become a carrier you will be assigned your own number ranges and you would need to comply with the NAD rules, ie you can only open numbers in a region where you have a local interconnect

Have fun reading NAD documents btw always fun.

hope this answers your questions