The Apple Personal Modem can't be used in Australia (or in many other
countries).
The modem may tolerate lower foreign voltages (as low as 50 Hz), but this
is not the primary problem.
Factors affecting modem operation vary from country to country. Some
countries confiscate computer equipment if you are found using a modem
within their borders. Other countries allow unrestricted use of modems, but
most have their own frequency standards.
The Apple Personal Modem adheres to Bell 103 and Bell 212 standards, but
these are U.S. standards -- most other countries do not meet these
specifications. There are also different standards for the grade (quality)
of phone lines. Modems must be able to use the physical media available
in the country of use.