Don't take this the wrong way, but your UK vodafone will work in NZ if you activate international roaming. Ring Customer Services or do it online. You'll probably be able to pick up an NZ Vodafone sim card at the airport when you arrive. If not, there are Vodafone shops in just about every main street and shopping mall in NZ.
If you really want an NZ number before you leave the UK, PM me and I'll send you one for a small fee.
