Google has unveiled its much anticipated mobile service in the US, partnering with Sprint and T-Mobile on an initiative called Project Fi that claims to be capable of switching seamlessly between WiFi and LTE technology.

As expected, the MVNO service will only be available at launch via Google’s own Nexus 6 Android device using a custom designed SIM. There is no word yet on an official launch date but Google is encouraging people to sign up for the service online.

Initial availability is on a selected basis; once an application has been received Google will respond within 30 days (criteria is based on date of application and network/service access in a user’s hometown). Users can transfer their current personal number over to Project Fi once signed up.

“Project Fi aims to put you on the best network wherever you go,” commented Nick Fox, VP of Communications Products at Google, in a blog post. “As you move around, the best network for you might be a WiFi hotspot or a specific 4G LTE network. We developed new technology that gives you better coverage by intelligently connecting you to the fastest available network at your location whether it’s WiFi or one of our two partner LTE networks.”

The Nexus 6 phone will switch between Sprint and T-Mobile US networks, depending on which carrier has the strongest 4G signal. When 4G isn’t available, the phone will drop back to a 3G/2G signal.

The Project Fi website states: “The Nexus 6 works with our unique SIM that lets you access multiple networks and has a state-of-the-art cellular radio tuned to work with different network types.” Google claims its software is optimised “to not put extra strain on your battery by only moving you between networks when absolutely necessary.”

However, Google has not revealed specific technical details on how the service works.

Google’s Fox said Project Fi has access to more than a million free, open WiFi hotspots. “If you leave an area of WiFi coverage, your call will seamlessly transition from WiFi to cell networks so your conversation doesn’t skip a beat,” he noted.

Fox added: “We also want to help phone numbers adapt to a multi-screen world. With Project Fi, your phone number lives in the cloud, so you can talk and text with your number on just about any phone, tablet or laptop.”

The no-contract service costs $20 a month for basic subscription (unlimited talk and texts, WiFi tethering, and international coverage in 120+ countries) and then users pay a flat $10 per GB for 4G data while in the US and abroad. Any unused data is refunded. For example, if a user pays for 3GB of data at $30 and only uses 1.4GB in any month, the user will receive $16 back.

Unlimited data plans are not supported. Neither are family plans. International data access is restricted to speeds of 256kb/s without incurring roaming fees.

“Here’s Johnny!!“
Outspoken T-Mobile boss John Legere couldn’t resist the opportunity to create some soundbites, describing its partnership with Google as a “no-brainer.”

“Anything that shakes up the industry status quo is a good thing,” he wrote in a blog, before taking a swipe at Sprint: “Since the cellular connection will be made based on network speed, we expect to capture the largest share of traffic coming from Project Fi customers.”

He added: “It’s been fantastic to pull together some of the biggest brains in tech to drive innovation that could directly benefit tomorrow’s American wireless customers. The carriers have dug in their heels and held US wireless back for too long. This industry needs all the fresh blood and fresh thinking it can get.”

The Project Fi website carries details of the network coverage, but it’s worth noting that Sundar Pichai, senior vice president of Google – who also heads up the search engine giant’s Android division – insisted at this year’s Mobile World Congress (MWC) that the service would be small scale and was not intended to compete with national operators.

“We are working with carrier partners on this, so they know what we’re doing”, he said at MWC. “Our goal is to drive a set of innovations which we think the ecosystem should adopt, and hopefully will get traction if our carrier partners think they’re good enough.”

Given the fact the service will only be supported by the Nexus 6 device at launch, initial subscriber numbers will likely be low compared to other MVNO services in the US.