Hi @dragonfly44 ,
Yes you can, however it would be expensive. Read about it here.
NEW ZEALAND (ZONE 1)
TALK: Make and receive a call:$1.00 / min
TEXT Send SMS:$0.50 / SMS Receive SMS:Free
DATA$0.50 per MB (charged per 10KB)
Beyond the data you might actually want, you also open yourself up to huge roaming charges if for some reason your phone's start using data unknown to you. Optus provides no way to limit that however if you have Android phones set local data limits and warning in your phone settings to avoid a huge run on data.
FWIW though, you're usually best off grabbing a local SIM when you arrive. It seems very straight forward in NZ, probably available at the airport but otherwise drop into a local Telco store and grab a data or data/calls SIM like this. Cheap and very safe.
Up to you if you want the call options but also suggest you check out WHATSAPP now and give it to your friends or kids you're likely to want to contact while gone - uses data only to make calls and send stuff. Handy for sending a photo of something to a bunch of people at once while away.
Note as a travel tip, if you use google maps check out downloading maps of areas you'll be in to your phone before you leave - added bonus is that the maps will then work even with no internet connection.
Note also that all the data free Optus streaming you might do isn't free overseas (Sport, Netflix, Music, etc.)
You can switch the SIMs in and out at any time BTW.