Google is set to unveil its MVNO service later today and charge customers for the amount of data they use, rather than sell data ‘buckets’, according to The Wall Street Journal (WSJ).

There is no official confirmation as to which network operators are selling wholesale capacity to Google, but previous media reports named T-Mobile US and Sprint.

T-Mobile US already offers its customers a way to avoid paying for data they don’t use through Data Stash, its data rollover scheme.

AT&T offers something similar, though the offer is not as generous. AT&T’s data rollover stretches only to the next month, rather than the maximum 12 months available with Data Stash.

Neither Verizon nor Sprint offer data rollover options, although a Google push on data-usage pricing might well encourage a re-think.

How widely the Google MVNO service will be available at launch is not known at this stage, although 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.

Indeed, according to unnamed sources cited by WSJ in previous reports, the service will be restricted to Google’s latest Nexus 6 smartphone at launch, and not work with any other Android-powered device, including older Nexus models.

Pichai stressed, too, that the MVNO would be primarily concerned with innovation, and develop new products and services that network operators might be keen to adopt.

One area of innovation flagged by the Android chief at MWC was making the experience of switching between cellular and Wi-Fi networks more seamless for consumers, as well as reconnecting dropped calls automatically.

“We are working with carrier partners on this, so they know what we’re doing”, he said. “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.”

The MVNO’s Nexus 6 phones, according to various reports, will dynamically switch between Sprint and T-Mobile US networks, depending on which carrier has the strongest signal.

There are no doubt industry fears, however, that a Google-run MVNO will not solely be about technical experimentation, but pose a retail revenue threat to network operators.

Sprint appears alive to that risk. According to media reports, the operator apparently inserted a clause into its wholesale arrangement giving it some protection if the Google MVNO proves highly successful. The contract, it seems, can be re-negotiated if certain thresholds are crossed, although it is not clear if these relate to traffic or subscriber volume.