Verizon Communications Inc., faced with losing a golden chance to gain full control of its wireless joint venture while financing is cheap, agreed to pay billions more than it had hoped to buy out its partner.

On Monday, Verizon said it agreed to pay $130 billion for Vodafone Group PLC's 45% stake in Verizon Wireless, the largest U.S. cellphone company. The cash-and-stock purchase would be the second-biggest acquisition ever, according to Dealogic. It would require an enormous amount of debt financing, including as much...