https://www.cnet.com/news/iphones-samsung-and-oneplus-devices-coming-to-google-fi-says-report/

Google Fi is also coming to iPhones, according to the reports, but the service is said to be in beta.

Google Fi switches your phone connection between Sprint's, T-Mobile's and US Cellular's networks depending on what's available. It also has access to networks in over 170 countries around the world.