According to a tweet from the official Project Fi Twitter account, it appears that there will be a mid-tier smartphone coming out later this year that supports the service. The tweet did also mention that it would be available from a Google partner, which doesn't really narrow down who might be making the device, but there have been rumors of LG making a phone for Google - which many thought was a Pixel device, it could be a Project Fi smartphone.
Currently, Project Fi is only available on a handful of smartphones, including the Nexus 6, Nexus 5X, Nexus 6P, Pixel and Pixel XL. Which are all sold at pretty high prices, and those that are looking to use Fi likely don't want to pay $500 or more for a smartphone. The Project Fi team stated that it has heard plenty of feedback for a mid-tier option for Fi. So it's good to see that it is going to be making one, or that it is already making one. Now this could be a smartphone made specifically for Project Fi, or it could just be something like the Moto G5 Plus made to work with Project Fi, since that device does already support all four carriers, it literally just needs the Project Fi software to switch between them and WiFi networks.
Project Fi launched after plenty of rumors, in 2015. It is an MVNO that uses the T-Mobile, Sprint and US Cellular networks. But the difference between Project Fi and other MVNOs (and why you can't just bring any old device into Project Fi) is the fact that it seamlessly switches between these three networks as well as WiFi and public WiFi hotspots - it uses a built-in VPN to protect you on open WiFi networks. That's something that most smartphones aren't able to do, which is why Project Fi has only had Google's own smartphones as part of the service. Hopefully that will change soon, as we have seen some other smartphones like the Moto X from 2015, work on Project Fi with very little issues. But now everyone is excited to see what this mystery device and partner is for Project Fi.