Interesting. One of the cool parts about Fi has been the seamless switching between different cell networks, which as I understood it was reliant on hardware that was only available on certain phones (e.g. Nexus, Pixel). Apparently if you use Fi on a device that does not support network switching, you'll just be on T-Mobile's network:

https://reddit.com/r/ProjectFi/comments/a17iq6/introducing_g...