Google has just launched the site for "Project Fi," its heavily rumored MVNO service. The service combines Sprint and T-Mobile along with Wi-Fi and will seamlessly switch between the networks. Google has an interactive coverage map here.

The up-front pricing seems pretty standard. It requires a "Fi Basics" plan, which is $20 a month for unlimited talk and texting, plus taxes. Data is an additional $10 per gigabyte a month. So a $20 basics plan plus 3GB a month would be $50, $5 more than Straight Talk charges for the same thing—but that's only if you actually use the data. The unique aspect of the billing is that you "never pay for unused data." Your account gets credited, in money, for data you don't use. The example shows an unused 0.6GB of data gets you $6 back, so credits aren't limited to 1GB increments; overages work the same way, with no extra fees. Google also allows Wi-Fi tethering.

The data works in "120+ countries," and it still costs the same $10 per gigabyte that it does in the US. The catch is that you're limited to 256Kbps, or about 3G speeds. International texts are unlimited, and international calls cost 20 cents per minute.

The big downside is that the service only works with the Nexus 6. The site says, "The Nexus 6 works with our unique SIM that lets you access multiple networks and has a state-of-the-art cellular radio tuned to work with different network types." Google is the only MVNO with control of the hardware, software, and network, which it has used to create "seamless" switching between networks. Google says calls can even move from cellular to Wi-Fi without dropping.

The company says it has "more than a million free, open Wi-Fi hotspots we've verified as fast and reliable." Wi-Fi connection is encrypted, allowing users to use public hotspots without being exposed to other users on the same network.

The phone number system seems to work a lot like Google Voice. Google will assign you a number, which will then ring on all of your devices that have Google Hangouts installed. Google has an app ready to go, of course. The Project Fi Android app will track data usage and allow users to switch plans and pay bills. It also gives access to 24/7 phone support.

The service is invite-only for now. Interested parties can punch their e-mail into the site and hope to score a golden ticket. We signed up and got an e-mail back saying, "As you know, we're sending a small number of invites each week, so hang tight. If you don't receive an invite soon, you'll get an update from us within a month."

Listing image by Google