Optus and Vodafone have confirmed it, Telstra's in its SDK as a compatible carrier and 3 is telling customers in store that they'll be releasing it after the July 11 Launch. The "it" in that last sentence is obviously the iPhone 3G.
But now Australian IT is reporting that Telstra will definitely be releasing the iPhone 3G, probably on July 22, with Uncle Sol likely to make an announcement as early as next week.
As Gus over at Lifehacker put it, Michael Sainsbury (who co-wrote the article) is insanely connected with people at Telstra, so there's a lot of credence to this story.
What does this mean for you? Well, if it's true, then Telstra's newtork will offer the best coverage for your iPhone, but it will almost certainly be the most expensive. If you ever need to travel to rural areas though, the big T is definitely your best choice.
Stay tuned for more info as it comes to light...