Project Fi, Google's MVNO cellular service has added US Cellular, the fifth-largest carrier in the US as the third network to its service. The service which was launched last year with the initial partners T-Mobile and Sprint.
U.S. Cellular offers service in 23 states with 4G LTE coverage for more than 99% of their subscribers, both urban and rural.
Google in a blog post wrote that, "..the majority of Project Fi usage occurs in areas where more than one of our partners offers LTE coverage. But factors like obstructions from nearby buildings can meaningfully impact the speed and coverage available from each LTE connection. By analyzing speeds from each network, Project Fi is able to predict the fastest network at your location — down to the city block — and automatically connect you."