I've been a Project Fi customer for about nine months and continue to use it as a secondary account for testing mobile devices. While I've seen solid coverage from the current T-Mobile and Sprint providers within Project Fi, it's great to hear the latest from Google that U.S. Cellular is now part of the Project Fi network.
U.S. Cellular owns and operates the fifth largest cellular wireless network in the US, with a reported 4.9 million customers in 23 states.
This new support for Project Fi is perfectly timed for my own usage here in Washington State as I plan to soon hit the western beaches and the eastern part of the state for fishing trips. Both of these future destinations show up on U.S. Cellular's coverage map as having the best coverage available on the network.
Project Fi will soon be able to analyze and predict the fastest of three cellular networks in your area, reportedly down to the city block, and provide you with service automatically. Google states that Project Fi customers have a connection nearly 99 percent of the time and spend about 95 percent of cellular time on LTE networks.