Under the expansion, iPhones and "the majority of Android devices" will be compatible with Google's service. That includes Google's straightforward pricing of $20 for unlimited talk and text and $10 per GB of data used up to 6GB. (It's free after that but speeds get heavily throttled at 15GB). It also includes international data coverage in 170 countries, spam protection, and a slew of other features offered by the service.
Google warns that while it's expanding its support, not all phones will get all of the benefits of Google Fi. The iPhone experience is in beta for the time being and will require additional steps to set up. Some features of the service, including the ability to seamlessly bounce between multiple cellular networks, will only be available to phones designed for Fi. That includes Pixel 3, 3 XL, 2 XL, Moto G6, LG G7, LG V35 and Moto X -- all of which are available directly through the Google Fi website. Google hasn't explained exactly how phones that aren't compatible with its network-switching feature will use Fi, but the company presumably feels confident it can provide reliable service without it.