As reported in the Dev Team IRC channel, Vodafone works. 3 works. (now just need Telstra + Optus/Virgin to be tested) 🙂
See original source here.
AFAIK – all Australian telcos who support the iPhone work. This includes Telstra, Optus/Virgin, Vodafone, and 3.
I’m still deciding… Do I really need my iPhone AS A PHONE when I go overseas?
It can function perfectly otherwise… Just needs Wi-Fi for data (which is admittedly scarce where I am going), but otherwise, it’s a small iPod.