iPhone 5 locked to Japanese network KDDI
You need to contact your new carrier &amp; see if they will unlock it. If the phone is legitimate, not stolen, doesn't have a blocked IMEI etc...

I can't say for NZ &amp; it appears every carrier treats it differently, but here's a guide on UK networks &amp; how they deal with it - might at least prepare you for the long conversation you might need with your own carrier.
http://www.macworld.co.uk/how-to/iphone/how-unlock-your-iphone-3501427/

There is an alternative of getting some backstreet phone shop to do it for you - but they tend to make you think it's illegal &amp; you pay accordingly for their 'expert' advice &amp; 'confidential service'.