I moved to Korea not to long ago and I asked Nokia about this. It more or less affects the warranty. As long as the frequency works in NZ you should be, ok. Also, the language piece was another part but you said, it didn't matter.

I use mine here in Korea as a PMP/Net(ish) book/camera. It doesn't work in Korea. Korea's phone system is strict. I thought about getting the Sony Satio instead since I am really only using it as a MP3/Camera phone. I loved the 12mp camera on the Sony Satio, but missed the Browser features.

Enjoy!