Google's Project Fi wireless service is now available without an invite.

The service launched in April as an invite-only plan, restricted to the Nexus 6. But now, anyone in the U.S. can sign up.

Project Fi is still restricted to Nexus 6, Nexus 6P, or 5X, but to sweeten the deal, Google is offering its Nexus 5X handset for a discounted $199 over the next month (down from $349), when purchased and activated through Project Fi. Unveiled in September, the LG handset sports an HD LCD display, USB-C port, fingerprint sensor, and 12.3-megapixel Sony camera sensor.

Rather than build its own network, Google opted to rely on Wi-Fi hotspots and cellular service from T-Mobile and Sprint for Project Fi connectivity. Phones connect to the strongest signal in a given area, and move between them seamlessly. You can shut off Wi-Fi like any other phone, though Google recommends keeping it on.

The program costs $20 per month for basic service (talk, text, Wi-Fi tethering, and international coverage in 120+ countries), and an additional $10 per GB (1GB for $10, 2GB for $20, and so on). Participants get a refund for any unused data at the end of the month.

Consumers can also request a data-only SIM for use in a compatible tablet or other data-only device. As with the phone plans, customers are charged $10 per GB of data, and only pay for what they use.

"We'd like to say 'thank you' to all our Project Fi customers for providing insights and feedback over the past 10 months," Product Manager Simon Arscott wrote in a blog post. "While Project Fi is still in its early stages, we're excited to welcome our next wave of customers and look forward to growing and improving together."

For more, see PCMag's reviews of Google's Project Fi.