Without any fanfare or announcements it seems the Amazon Appstore is now available to Australians without the need for proxies, VPNs or dodgy overseas addresses. To install the Amazon Appstore on your phone and start taking advantage of the famous ‘Free App of the Day’, head on over to the Get Started page. You will also need to set up an Amazon account, but feel free to use your Australian address and Australian credit card. You may note there is a large notice reading “The Amazon Appstore is only available to customers located in the United States”, you can ignore that for the time being, I tried to install this myself and it worked fine.
EDIT: And looks like it is region locked to the US again, it was fun while it lasted.