Project Fi is a wireless service program backed by Google to deliver a fast, easy wireless experience in close partnership with leading carriers, hardware makers, and us users. See how it all works in the video below.
The service is currently available in the US and users with Nexus 6. Although if you have a registered number with Hangouts app you can use this service on any device. The Plans are really competitive with other carriers and the only thing that will keep it going would be the connectivity. Get your invite here.