According to this report, the iPhone's bundling to one carrier may breach Australia's competition laws:
If Apple...lock the iPhone to a single network in Australia it could fall foul of the Trade Practices Act provision dealing with third-line forcing.
This could cause delays in the iPhone's Australian release. Similar legal issues were encountered by Apple in Europe where the iPhone is now available on any network in France after initially being tied to one provider. I've seen so many of these gadgets (imported from the U.S.) walking about in Australia that its painful.