Verizon Communications Inc., the nation’s largest wireless carrier, agreed to acquire fiber-optic networks from Carl Icahn’s XO Communications LLC for about $1.8 billion to add Internet bandwidth for corporate clients.

Verizon will also lease wireless spectrum from closely held XO, with an option to buy the unit that controls the airwaves by the end of 2018, according to a statement Monday.

The carrier, which gets about 10% of its revenue from its enterprise business, will acquire more infrastructure to sell backhaul, the circuits that allow mobile-phone calls to be routed along landline networks. Wireless companies try to switch their calls to landline networks to lower the calls’ cost.

XO’s fiber facilities also will help make Verizon’s cellular network denser, the company said.

Icahn, XO’s sole shareholder who began purchasing senior debt in 2001, said in a statement that the sale doesn’t represent a “significant annualized return” on his investment but the “best achievable outcome for the company’s customers, employees and owner” in today’s market.

Citigroup Global Markets Inc. acted as Verizon’s financial adviser while Debevoise & Plimpton LLP provided legal counsel. For XO, Evercore served as financial adviser and Thompson Hine LLP provided legal counsel.

The transaction is expected to close in the first half of 2017, Verizon said.

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