How do I place a call to Australia?
This is one way:
Republic does not have any international calling plans, so you’ll need a third party app or service [like Google Voice, Vonage] or an international calling card like @billg suggested, there also this on the Republic’s Wiki page Adding International Calling to Your Republic Phone | Republic Wireless Wiki | Fandom powered by Wikia
Conversely – and maybe implausibly – if you send a republic Wireless phone to someone you would wish to speak with in Australia you may call that phone and that phone may call back here to the US over Wi-Fi. As noted there is no international cell service for it.
If possible remove the battery before shipping. If the phone is sealed run it down to about 40% charge or even to 20% and be sure it’s turned off as well. You may have seen article about exploding phones, tablets or e-cigs. Lithium batteries can be volatile.
I realize this is the opposite of what you asked about but some problems yield to reversed solving. Talking to a foreign exchange student or someone on an extended trip are a couple of examples.