Project Fi combines local Wi-Fi with the mobile data network to give you telephone and Internet access at a low price, $20/month plus $10 per gigabyte of data. That’s probably a better rate than you’re now getting on your cellular plan.
Google has teamed up with Sprint and T-Mobile to offer the telephone service. From what I understand, the Project Fi technology chooses between using Wi-Fi or LTE (cellular) depending on which is fastest. That saves money. I don’t believe Google is providing the Wi-Fi service; it’s local. But apparently you must be a current Sprint or T-Mobile subscriber to use Project Fi.
My only burning question is whether to pronounce it fee or fie?