By Jonathan Davies

Google has launched details of its mobile network Project Fi in the US.

The search giant will use voice and data capacity from Sprint and T-Mobile, and existing WiFi hotspots.

Only users of the Nexus 6 handsets will have access to the Project Fi network.

One tech expert said that reliance on another company's infrastructure may limit the impact that Project Fi has.

"The example of MVNOs in the US and elsewhere suggests that it's hard for their operators to dramatically change the industry because of their nature," said Ian Fogg from the IHS Technology consultancy.

"But the past isn't always a guide to the future.

"No-one would have thought that a handset manufacturer could transform the mobile industry by teaming up with one network - but that's what happened with Apple and AT&T when the iPhone launched.

"And Google itself has repeatedly shown that it is capable of changing the direction of an industry by entering it."

On its blog, Google said: "As you go about your day, Project Fi automatically connects you to more than a million free, open wi-fi hotspots we've verified as fast and reliable.

"Once you're connected, we help secure your data through encryption. When you're not on wi-fi, we move you between whichever of our partner networks is delivering the fastest speed, so you get 4G LTE in more places."