i would be checking to make sure your phone isn't locked to your network in AU (and that it runs on the right frequency to work in NZ) - and then, as tracey suggested - grab a pre paid sim card over there. you don't want everyone contacting you while you're away, so it's not like you need to tell heaps of people the number once you get there - and it will be cheaper for you that way. it will also stop people calling "just for a chin wag" cos they'll be paying for an overseas call

good luck - and enjoy your holiday