You probably have your answer now so this is more for people still looking for a solution. The free Temando magento shipping extension has a new function called the Rules engine.
With the rules engine you can set up rules based on post code ranges. You can assign carriers to the ranges and set up shipping rules around them. This way you can set up your choice of shipping taking advantage of Aupost, fastway, startrack, tnt.
The best part is you can nominate the text that is displayed on the estimate shipping page and at the cart level. For example you could write \"standard delivery 2-4 business days\” or you could write \"Overnight shipping\” its your call.
Why is this helpful ? Well have a look at one customer woolworthshampers.com.au it takes advantage of the temando magento rules engine by getting the best courier for specific areas, all automated.
Another feature is the multi origin feature - this feature helps you drop ship or assign certain stock to a 3pl or suppliers location right from your magento admin section. Have a look at some of the screenshots at http://temando.com/magento
Hope this helps with your Magento shipping in Australia