Hi @CSS33 , yikes the charges would be an unpleasant surprise for sure. When I roam, I turn my device to airplane mode and the manually turn on WiFi. I also remove my SIM card as an extra measure. As soon as you turn on your device when roaming, it automatically tries to register on a network and that triggers a roaming activity. You can also set your roaming to off or ask first. If you need help with that, let us know.
The surest way is remove the SIM card (put it somewhere safe like between your phone and the phone case) and leave Wi-Fi turned on. Hope that resolves the roaming fees for you.