Google's own MVNO monthly cellular service. Click below for $20 off your first month's service.
About Google Fi
Google Fi is a MVNO with the somewhat unique ability to operate across multiple carriers (T-Mobile and Sprint being the major providers) as well as offload calls to Wi-Fi when available. For the end user, this means better connectivity as the phone seamlessly switches among multiple connections to provide the best service, but comes at the cost of a limited number of devices. That being said, if you wish to forgo the carrier optimization described above, the Google Fi SIM seems to work with other devices as well.
Although capable of working on other phones, I much prefer using the Google approved devices (Nexus and now Pixel) as they provide the cleanest Android experience free from the OEM and carrier adulterations. The fact that I was already using a Nexus device with another MVNO carrier, and the generous discounts Google Fi offers towards Nexus and Pixel phone purchases, made switching to Google Fi completely worth it. Although I had no service problems to speak of, the Nexus/Pixel phones are sold unlocked so switching back after receiving your discounted phone is a non-issue.
I’ve been using Google Fi for over a year, including several international trips, and the service worked well and without issue. I did contact support for a replacement Nexus 5X device (the LG-produced device had a defect that caused many devices to boot-loop) and was issued a refurbished Nexus in short order. I would say existing MVNO users, international travelers, users already invested in Google’s ecosystem, and users that are not data-heavy could benefit from trying out the service.