Just to clarify, this is not an official street date break but, as reported by Vooks, Gametraders is selling EU, imported versions of Ocarina of Time in their stores, a week ahead of the game's official release date in Australia.
The EU version will work in your Australian 3DS, so there's no issues there.
It's interesting - while most retailers wouldn't attempt this for fear of ruining established relationships with publishers, Game Traders has been known to stock grey imports of games instead of buying stock normally at cost price. Technically, from my understanding, this is illegal since the games don't have Australian classifications on the box - but it's the job of the police to enforce this, and doing so would probably be a colossal waste of their time. We suspect the only people who will have a problem with this is Nintendo themselves.
So, if you feel like picking up a copy of Ocarina of Time on the 3DS early, you know where to go! Just be aware that you won't be able to redeem your free Ocarina of Time soundtrack.