Google Inc. unveiled a U.S. wireless service, called Project Fi, as the Internet giant looks for new ways to extend its reach in mobile.

The national service will be available in certain areas around the country, the company said in a blog post on Wednesday. It’s being offered in partnership with Sprint Corp. and T-Mobile US Inc. networks, and will let customers pay $20 a month for basic features such as talk and text, plus a flat $10 per gigabyte for data in the U.S. and abroad. Users will get credit for unused gigabytes.

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The technology works via wireless carrier networks or through Wi-Fi. The service will begin on an invitation-only basis. Customers can request an invitation through Google’s website.

“Project Fi enables us to work in close partnership with leading carriers, hardware makers, and all of you to push the boundaries of what’s possible,” the company said in a blog today. “By designing across hardware, software and connectivity, we can more fully explore new ways for people to connect and communicate.”

Selling its own mobile-phone service could enable Mountain View, California-based Google to add customers for its Android operating system, used by many different device makers, and make it easier to serve those users advertisements via smartphones and tablets.