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Google opens up Project Fi to all -- but just for today

The Internet giant makes it easier to try its new wireless service, which relies on a combination of Wi-Fi and cellular service.

If you've been thinking about checking out Google's Project Fi wireless service, now is your chance.

The Mountain View, California, Internet search titan said Monday it's giving out "instant invites" to the service for the next 24 hours. Interested users can sign up directly on the company's website.

Project Fi is Google's attempt to shake up the wireless industry with cheaper plans that also reduce the strain on carrier networks. The service uses a combination of cellular coverage from T-Mobile and Sprint and local Wi-Fi networks. It has largely been an experiment, with the service available only by invitation and only on Google's Nexus 6 smartphone.

Project Fi uses Sprint's and T-Mobile's networks if Wi-Fi is unavailable. Josh Miller/CNET

Google is opening up the service as its new smartphones hit the market. Last month, Google said the Nexus 5X and Nexus 6P would support Project Fi. The Nexus 5X went on sale today.

What's most likely to attract consumers to try Project Fi is its low cost. Users in the US pay $20 a month for unlimited calls and texts. Adding data costs $10 for each gigabyte used. If customers don't use their allotted amount in a month, they get a credit in the form of more data.

Google hopes to upend the traditional carrier business model by using more than a million Wi-Fi hotspots that provide cheap access to the Internet and using cellular service to fill the gaps. A key aspect of Project Fi's service is technology that determines which network offers the best connection. It can seamlessly switch among these networks if one connection weakens.

This is similar to other services from companies like Republic Wireless, Scratch Wireless and FreedomPop. They were among the first companies to build mobile businesses that use free Wi-Fi networks but then switch to cellular service as a backup when Wi-Fi is not available.

Project Fi has gotten mixed reviews. CNET editor Lynn La reviewed the service this summer in San Francisco and found it to be slow compared to pure cellular services.

CNET's Sean Hollister contributed to this report.