In fact Garmin have a truly strange business model. You can't buy a serial unlock from their website, you have to buy a physical card with the software loaded on it. You will probably have to pay a lot for a NZ map as well, when there is perfectly a legit open source map from the NZ open GPS project. If you take the software off that card using the Garmin Unlock Utility, which can be found on the web, and put it on a larger card, then you violate the licence.
It seems absolutely mad to me. To have your phone working well you obviously want a big card for lots of songs/media. You don't want to have to swap the card just for navigation.
Oddly enough, the Garmin Unlock Utility will also unlock the software that you have downloaded from the net. I'm sure Garmin would make a lot more money if they just made it easy to pay them some money for a legit unlock code. Once it is unlocked it will pick up the intermediate GPS driver.