How much tax do I have to pay for an iPhone that I receive by mail from the US to Australia?

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I am buy an iphone 3G 16GB from an online store in USA. The shipment cost quoted is 45 USD. And will be shipped by Fedex/DHL. How much tax do I have to pay for a single unit? How does the tax calculate?
Thanks very much for your answers.
BTW, the phone will be officially unlocked from [...]