You have to apply for a radio operator license or, if you are not a US citizen or green card holder, a restricted radio operator license.
You can do this through the FCC website. It's a little tricky to find the right link but it's there.
However, this is only required to fly US registered aircraft outside the US. If you fly a VH registered aircraft you need to obtain certificate of conversion from CASA anyway. This is only if you want to act PIC.
Remember, logging and acting PIC are two very different things. If you pass by Perth drop me a mail.
Cheers,
Space