Unless they somehow restrict this is to Milestone, it looks like this functionality may be enabled for all Android phones in NZ from about that date. Fingers crossed.
Turn-by-turn navigation was enabled for Canada and many European countries a week or so ago.
Quoting text extract here for posterity:
"Turn-by-turn navigation instructions
A signature feature of Android 2.0 is a new version of Google Maps with voice-enabled turn-by-turn directions, a feature Telecom confirms will be available with the Milestone's local release (which will run on Android 2.1; a welcome climb on the Xperia's 1.6; the most up-to-date version is 2.2)."
Unless that is a hopelessly lost mash-up of boilerplate from some other source, it's looking good for turn-by-turn nav. (I don't recall if that was not operational on Android v1.6. I've been playing with v2.1 ROMs since late last year.)