Hi Mimi. Thanks for coming through. Yes, you'll be charged for any usage while overseas, which includes calling back to Australia from Europe. I recommend taking up the Day Pass, in your 24/7 app; which will limit your daily spend on calls/SMS in eligible countries to $10 each day, and only activates on days you use the service. Its the best way to balance peace of mind around charges; with the convenience of staying in touch when need be.
More info here - https://tel.st/2ml7h - Please let us know if there's anything else we can clarify. - Matthew.