Verizon (NYSE: VZ) is offering to double the monthly mobile data allotments for new and existing wireless customers in the Northeast U.S. who also sign up for the company's FiOS service.

The carrier quietly launched a regional, limited-time promotion that doubles the monthly data buckets for users with its XL or XXL plans who sign up for FiOS, the operator's fiber-based wired Internet service. The offer increases the XL plan to 24 GB per month and the XXL plan to 36 GB per month.

The promotion wasn't officially announced, but a Verizon spokesman confirmed the campaign to FierceWireless. Verizon isn't saying how long the offer will last, and the spokesman declined to say whether the carrier intends to roll out the campaign to more locations where it offers FiOS.

Verizon recently agreed to sell its wireline properties to Frontier in California, Florida and Texas, and after that sale closes Verizon's FiOS footprint will be mainly concentrated in the Northeast U.S. And Verizon has said that area is underpenetrated when it comes to FiOS: "If you're going to launch broadband to the home, you're either going to pick the East Coast or the West Coast, and we have the East Coast population density from Washington, D.C. to Boston," Verizon CFO Fran Shammo said at a recent investor conference. "It's a very good footprint for us and we believe the property we have are still underpenetrated."

The nation's largest mobile operator is clearly hoping to use its leverage in mobile to shore up revenues in a fixed-line broadband market in which telcos are struggling. Verizon's broadband business saw only 23,000 net customer adds during 2015, and the nation's top telcos lost a total of more than 185,000 subscribers last year (cable operators, meantime, managed to add 3.3 million broadband customers in 2015).

For Verizon, the carrier added just 99,000 new FiOS Internet subscribers in the fourth quarter, far fewer than the 145,000 it reported during the same period a year earlier.

Verizon's promotion is just the latest example of a mobile network operator bundling and cross-promoting to build businesses on multiple platforms. For example, AT&T (NYSE: T) launched a campaign earlier this year offering unlimited monthly data packages to users who sign up for its DirecTV service. The company said last week that more than 2 million users have signed up for the plans, which launched only two months ago.

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