Hi
Add on's only work when EU Roaming... so using your phone in Australia will incur charges that will come out of your credit balance...
You will also have to have a 48 membership of choice running too.
When you're roaming in Australia or New Zealand you'll pay:
Making calls and calling your voicemail €3.09 Receiving calls €2.19
Sending texts 39c
Receiving texts Free
48 also do not support Data/Internet Roaming as it is so expensive.
Wifi all the way!
Hope this answered your query in full.
🙂