To prevent unexpected international roaming charges, you must adjust your phone's cellular settings before you land. On an iPhone, go to Settings > Cellular (or Mobile Data) > Cellular Data Options and toggle Data Roaming to OFF. You can also turn off "Cellular Data" entirely to be safe. On Android devices, the path is typically Settings > Connections > Mobile Networks, where you can toggle Data Roaming OFF. To be 100% sure, you can also put your phone in Airplane Mode and then manually re-enable Wi-Fi; this prevents your phone from even connecting to a foreign cell tower while allowing you to use hotel or cafe internet. Additionally, you should disable "Background App Refresh" and "Automatic Downloads" in your app store settings to stop apps from consuming data in the background. In 2026, many travelers also find it helpful to contact their carrier to place a "roaming block" on their account or to switch to a travel-specific eSIM (like Airalo), which uses a fixed data plan and prevents your home SIM from ever being charged.