As it is with SIP Accounts, your Accounts are connected to the cloud and not to a physical exchange. Due to that fact, we are unable to determine when a number is dialled is a local call or not.
However, with the @voice powerful translation rules, you as the service provider can set this up for the Account in Account Settings > Advanced Settings > CLD Translation.
If you want to provide local calling, you can use the below CLD Translation Rule. The below example is to provide local calling for Victoria where it will transform any 8 digit number dialled and insert a 613 at the front. If it is for NSW, just change the 613 in the code below to 612.