Best answer: Almost any unlocked phone will work on Fi, but phones that weren't specifically designed for Fi may miss out on certain features like Google's VPN and network switching.
Google Store: Pixel 3 ($799)
What phones work on Fi?
When Google Fi originally launched under the name Project Fi back in 2015, it was only available for the Nexus 6. As consequent Nexus and Pixel phones came out, Fi continued to expand, eventually reaching non-Google phones like the Moto G6, Moto X4, and LG G7 ThinQ. But even with a small list of sanctioned devices, Fi still wasn't compatible with the vast majority of phones in consumers' pockets.
Google Fi is open to just about any unlocked phone now, even iPhones.
Part of that is because of Fi's use of both T-Mobile and Sprint towers (among others) for its service, and its automatic network switching based on the best available signal. For a device to offer the best possible experience on Fi, it would need to support both networks — though you were still able to pop an activated Fi SIM into an unsupported GSM phone and use Fi on T-Mobile's network.
As of late November 2018, Project Fi was finally rebranded to Google Fi, and Google began officially supporting Fi on virtually any unlocked phone. GSM and CDMA phones alike can finally be used on Fi — even iPhones — with a few exceptions. In most cases, your phone should be compatible with Fi so long as it's not locked by the original carrier, but to be safe, Google has a compatibility checker on the Fi site that you should use before ordering a SIM.
What makes a 'designed for Fi' phone special?
Even though most unlocked phones will work just fine on Google Fi these days, you'll still get a few perks for using a phone specifically designed for Fi. Only Fi-optimized phones can make use of Google's network switching technology, which can mean significantly better service in areas where one of Google's network partners has better coverage than the others.
Phones 'designed' for Fi get some extra features, so you should consider those first.
Phones designed for Fi are also the only ones that will automatically connect to the over 2 million secure Wi-Fi hotspots that have been approved by Google to save on data usage and will switch away from Wi-Fi up to 40 percent faster when the connection is poor. Maybe most importantly, they're the only phones with the option of encrypting all data through a Google-run VPN.
If you're on a Pixel 2, 2 XL, 3, or 3 XL, you also get the added benefit of an integrated eSIM that lets you use Fi without having to wait for a physical SIM to arrive in the mail. Just keep in mind that you can still only use one network at a time — you can't use both a physical SIM and the Fi eSIM at the same time to achieve a dual SIM Pixel.
Ultimately, Google Fi is a great prepaid network regardless of which phone you're using it on. While there are still advantages to using a phone specifically made for Fi, we're just happy that it's finally open to any device that supports its network partners.
The best way to experience Google Fi
The Pixel 3 isn't just one of our favorite phones. It's the best phone for Google Fi — you can get up and running immediately thanks to the built-in eSIM, and it seamlessly switches between cellular and Wi-Fi networks to ensure the best connection at all times.
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