This might inspire a lot of wireless providers, and consumers, to rethink their mobile phone plans: Google formally unveiled today its long anticipated wireless service, called Project Fi. It costs $20 a month, and will route calls via WiFi, Sprint, or T-Mobile — whatever’s fastest.

The fee includes talk, text, Wi-Fi tethering and coverage to more than 120 countries. It’s an additional $10 for 1 Gb of cellular data, or $20 for 2 Gb, etc. — and you get a credit for the data that you don’t use.

Like a lot of Google initiatives, the company is limiting the roll out. People can ask for an invitation here . For now it also only works with Nexus 6 phones.

But Consumer Products VP Nick Fox says in a blog post that the company will “work in close partnership with leading carriers, hardware makers, and all of you to push the boundaries of what’s possible. By designing across hardware, software and connectivity, we can more fully explore new ways for people to connect and communicate.”

Google execs may have more to say on Thursday, when the company releases Q1 earnings and holds its quarterly conference call with analysts.