I would expect this to be fine. The charger contains a transformer which converts the supply voltage from the wall socket into the voltage required by the phone to charge. I couldn't say for sure, but it stands to reason that they'd build all the phones the same and build different chargers for different countries (seeing as there are different power socket pin configurations and different voltage supplies in different countries). It's most likely that all chargers would convert from different supply voltages to the same output voltage for your phone, so as long as you have an Australian charger I don't see why you'd have a problem.