Global phone service is generally something no one wants to talk about. In each of the cases, free roaming is covered while you're visiting.
First off, Project Fi is now available to use in 37 additional countries - meaning that subscribers now have full coverage in over 170 different markets. The list is indeed long, and can be seen in full over on Project Fi's worldwide coverage page. Now might be a good time for you to take a look at Project Fi. Any Gmail messages related to such travel will be tagged with a Project Fi notification regarding that destination. Google also revealed today that it will begin using your worldwide bookings from Gmail to prepare and send reminder notifications to your phone a few days before you leave.
Being able to determine if a country you are visiting is supported by Project Fi is important, as it can help with planning.More news: Germany coalition: SPD's Schulz gives up cabinet role to save deal
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Of course, that's not to say that there's zero risk of runaway charges while using Project Fi overseas.
They will see a notification in the Project Fi app shortly before their trip to see their coverage options and costs.
If you're set to travel and want to know if your destination is covered by Fi, the answer is most likely yes.