The Apple Support Communities are an international user to user technical support forum. As a man from Mexico, Spanish is my native tongue. I do not speak English very well, however, I do write in English with the aid of the Mac OS X spelling and grammar checks. I also live in a culture perhaps very very different from your own. When offering advice in the ASC, my comments are not meant to be anything more than helpful and certainly not to be taken as insults.
With the advent of the announced iPhone 5, there are three models to choose from, so you need to find out what the telco requirements are in Australia and make sure that you buy the phone that meets those tech requirements as an unlocked iPhone from Apple. But some folks report warranty issues with taking iPhones from one country to another. If the phone needs to be repaird or replaced, Apple may require that the phone be returned to the country in which it was bought for service.