Project Fi, the wireless service launched by Google this past April, offers an attractive set of innovations and a straightforward pricing model. Its invite-only sign-up process and the fact that it only works with a single handset - the Nexus 6 - has unfortunately kept many prospective customers at bay.

That's all changing today.

For one day only, Google is opening the flood gates and allowing anyone in the US to sign up for Project Fi. All you need to do is head over to the Project Fi website to get started.

The catch? Google is only pardoning the invite-only sign-up process today to celebrate the launch of the Nexus 5X. If you're interested, you'd better register for the service ASAP. Both the Nexus 5X and the Nexus 6P are compatible with Project Fi.

For those unfamiliar, Project Fi is the name of Google's new wireless mobile service. Instead of launching its own nationwide network of cellular towers, the search giant is acting as a mobile virtual network operator (MVNO) in which it buys airtime and data from an existing wireless carrier and rebrands the service as its own.

It's a common practice although Google's approach is quite unique. Whereas other MVNOs partner with a single provider, Project Fi leans on service from both Sprint and T-Mobile - intelligently selecting the best network given your current location.

Project Fi starts at $20 per month which includes unlimited domestic talk and text, unlimited international texting, unlimited Wi-Fi tethering and discounted calling rates to more than 100 countries. Data is priced at $10 per GB with a minimum of 1GB per month (so really, you're paying at least $30 per month).

What makes the service incredibly appealing, however, is the fact that you only pay for data that you use. Any unused data at the end of the month is credited back to you in cash.