Toxa, in NZ the regional area codes are two digits eg (09) for Auckland or (03) for the South Island. The code for Mobile phones are (025) or (021), or there is a new code now as well I think - (023) perhaps? Mobile phones are not tied to any particular region, unlike in the US, so there is no 'area code' as such for mobiles.
From inside NZ, even if they were standing in the same room as you, people would have to dial 021 xxx xxxx to reach you. From outside NZ, they would dial +64 21 xxx xxxx.
Hope this helps. And does this mean that you and the ultra-glam ToxaGirl are currently gracing New Zealand with your presence?