Press release 3 and a half years ago https://www.geekzone.co.nz/content.asp?contentid=17191 says
“We’ve continued to develop and invest heavily in our 4G network since we launched the service two years ago – including constantly increasing our population coverage – and we’ll continue to do so as we work towards the commercial launch of VoLTE in the near future.”
So - how far away is the near future?