Launched in 2015, Google's Project Fi has to be one of the most technically ambitious wireless services available. That's because Fi as a service doesn't just have one carrier partner, it has three: T-Mobile, Sprint and US Cellular. Each Project Fi phone is meant to switch between those three networks depending on which has better coverage where you happen to be at the moment. Having used the service since launch, I can say those transitions are seamless. You'll never notice them yourself, either -- as complicated as it sounds, the whole thing just works.
What's the big deal?
Here's how it works: You'll pay $20 for unlimited minutes and messages, but data costs are considered part of a separate bucket. While Google doesn't specifically use the word "unlimited" to describe its plans, the company charges you $10/GB until you hit 6GB of data use in a month. After that? They stop charging you altogether. Even better, data speeds stay nice and fast until you hit the 15GB threshold, which Google says only applies to 1 percent of current Fi users. After that, you're kicked down to EDGE speeds until your billing cycle resets or you agree to pay $15 for every gig of data past 10GB.
That might sound convoluted, but the results aren't: Unless you're the type of person who needs loads and loads of high-speed data, your plan won't cost more than $80/month. (The usual taxes and fees might put you over the top, though.) Even better, you only get charged for the amount of data you actually use, so you'll wind up with a smaller bill on months where you don't need your phone as much.
If you're a frequent traveler with a compatible phone, Project Fi might be invaluable. Partnerships with carriers in over 170 countries mean that in almost every case, you'll be able to turn on your Fi phone once you've landed and start Instagramming every little thing. Each gigabyte of data consumed abroad will set you back $10, and calls made overseas still cost the standard (and slightly eye-watering) 20 cents a minute. That said, there's nothing stopping you from chatting up friends at home through Skype, WhatsApp or Facebook voice calls instead of traditional phone calls.
What kind of phone can I use?
Because of the way these phones have to switch between T-Mobile and Sprint towers depending on which are stronger in a given area, Project Fi has the most limited selection of smartphones on offer. At the time of publication, Google officially supports the Nexus 5X, Nexus 6P, all generations of the Google Pixel, the Moto X4, the Moto G6, the LG G7 ThinQ and the LG V35 ThinQ.
I say "officially" supports because you can actually throw your Project Fi SIM into just about any unlocked GSM phone and get most of the same functionality -- you're just stuck using one carrier instead of two. This isn't a terrible way to go if data use is your primary concern, but the sticking points otherwise add up quickly. In my experience, at least, every phone call I received appeared to originate from the same California phone number. Others have reported degraded connection and call quality too, so ultimately you're better off sticking to Google's approved hardware.