Pretty much all phones will work in Oz, as long as they are unlocked to all networks.
I have an iPhone, and I had it unlocked by Orange before I left the UK, and it works fine. You'd probably be better off waiting until you got to Oz to buy an iPhone though, as I believe that unlike most of Apple's products, the iPhone only has a UK warranty if bought in the UK.
Also, Apple's products are better value in Oz than in the UK.
An iPod Touch isn't really worth the money as it's pretty much the same as an iPhone apart from lacking in being able to call and text. An iPhone has the same capabilities as a Touch, so as the iPod software.