Project Fi, Google's MVNO cellular service, launched last year with the unique ability to switch between multiple networks—T-Mobile and Sprint. Today Google announced that it is adding a third network into the mix—US Cellular. US Cellular is the fifth-largest carrier in the US, and Google says the company's LTE service in "23 states, both urban and rural" will be merged into the Project Fi network.

Project Fi uses special SIM cards and radios to work as a "network of networks." Fi-compatible phones measure the available connections from participating cellular networks and switch to the fastest one on the fly. With the new addition, Fi phones will now pick the fastest network from T-Mobile, Sprint, and US Cellular. The downside is that you actually need a Fi-compatible phone, which right now is the Nexus 6, 5X, and 6P.

The service also provides a ton of Internet-centric features, full functionality over Wi-Fi, online voicemail, texting from other devices via Google Hangouts, call forwarding, and a sweet mobile app. Voice and text on Fi is unlimited, and data charges work on a flexible system where users are only charged month-to-month for what they use, at a rate of $10 per 1GB.

Fi users won't need to do anything to get the enhanced coverage. Google says "U.S. Cellular coverage will be automatically rolling out to all users over the coming weeks."