It’s a good idea to turn off data roaming on your iPhone if you want to avoid using data while traveling internationally.

You can turn off data on an iPhone all at once, for specific apps, or by turning on Airplane Mode through the Control Center.

Turning your phone's connection off and then back on is the quickest and easiest way to try and fix your signal woes. If you're moving around from one location to another, toggling Airplane mode ...