U.S. cable giant says the success of its new service will be measured by its impact on its cable customer churn rate.

After what feels like decades of build-up, Comcast late on Thursday finally detailed plans to address the mobile market in a bid to fend off growing competition from the likes of AT&T and Verizon.

Called Xfinity Mobile, the service runs on Verizon’s 4G network, but aims to make extensive use of WiFi, with devices automatically connecting and authenticating on one of Comcast’s 16 million public hotspots whenever the customer is range.

Comcast was also one of the participants in the recently-concluded 600-MHz incentive auction; however, the assignment phase of the process is still ongoing, which prevents Comcast discussing any plans around using its own airwaves.

Dave Watson, CEO of Comcast Cable, said that while Xfinity Mobile does give it an opportunity to attract new subscribers, it is primarily a defensive play.

"Customer loyalty will be how we define success," he said on a Webcast.

Indeed, to be eligible for Xfinity Mobile, customers must already be signed up to one of Comcast’s home broadband or TV services. That limits the availability of Xfinity Mobile to the company’s cable network footprint.

Nonetheless, Watson said this still gives Comcast an addressable market of 130 million consumers.

Xfinity Mobile is no loss-leader either.

"Even at limited scale, we expect to have positive economics on a per-customer basis," Watson said.

Comcast’s move into mobile comes as U.S. telcos, particularly AT&T and Verizon, seek to muscle in on media.

AT&T, which already operates U-verse TV and owns DirecTV, is in the process of trying to acquire content conglomerate Time Warner.

Verizon has its Fios TV service and is attempting to crack the mobile video streaming market with go90.

Meanwhile, T-Mobile US doesn’t have a fixed-line business, but it does have Binge On, which enables customers to watch video from participating services, like YouTube, Netflix, and Amazon, among others, without it counting against their mobile data allowance.

These three players are capitalising on the growing trend of consuming content on the go, putting traditional TV providers like Comcast under pressure to respond.

Comcast’s move in the opposite direction has been a long time coming.

Comcast was one of several investors in WiMAX operator Clearwire in 2008. In 2009, it started reselling Clearwire’s Clear mobile broadband service alongside its fixed-line offerings. However, it was not a full mobile service, it only offered data, not voice, nor messaging. Clearwire was eventually taken over by Sprint in 2012, and Comcast shut down its Clear service in 2015.

Comcast has also had an option to offer MVNO services via Verizon’s network since 2012. It was an obligation imposed on Verizon by the Federal Communications Commission (FCC) in return for approving its proposed acquisition of $3.9 billion worth of spectrum from Comcast and rival cablecos Cox, Time Warner Cable, and Bright House Networks.

Despite the late arrival in mobile, "we do have confidence in our ability to compete in a crowded marketplace," said Comcast’s Watson.

He pointed out that Comcast was not the first to offer fixed broadband and voice services; neither was it the first to address the business market, nor the home automation and security markets.

"In every one of these we were not the first in these categories, but we’ve had success in all of them," Watson said.

As well as enabling cable customers to access content on mobile devices, Comcast also hopes to tempt prospective wireless users with a flexible pricing strategy.

Customers can opt for an unlimited tariff that costs $65 per line for up to five lines. Customers signed up to Comcast’s top-end X1 cable TV and broadband packages will pay $45 per line.

"We do that, because these customers are very valuable to us," said Greg Butz, who has been appointed president of Comcast Mobile. "It’s a great deal for the customer, but it’s good business decision for us."

Alternatively, Xfinity Mobile customers can choose to pay $12 per gigabyte of mobile data.

Here is the clever part though: if a customer is paying by the gigabyte, but realises they are consuming so much data that they would have been better off on an unlimited plan instead, they can switch to one the following month without incurring any charges. They can also switch back to a per-gigabyte plan the month after, should they wish.

What’s more, this flexibility applies on a per line basis, so one, data-hungry member of a family can switch to an unlimited plan, while everyone else keeps on paying per gigabyte.

"If you just want to get started with us because you don’t know what your data usage is…it’s not a problem…we’ve got you covered," said Greg Butz, who has been appointed president of Comcast Mobile.

Whether subscribers are on an unlimited tariff or pay per gigabyte, they get unlimited, nationwide voice and texts.

Xfinity Mobile is due to launch in the coming months. In the meantime, Comcast is running a trial service available to employees.

The cableco made it clear that it is in it for the long haul.

"Things don’t happen overnight. We will make adjustments over time," said Watson.