Vodafone Group is in talks to sell its 45% stake in Verizon Wireless for about $130bn (£83bn).
Verizon Wireless is the second-largest mobile network operator in the US with about 100 million customers.
If the deal materialises, it could be the third-biggest deal of all time.
Funds raised through the sale should help Vodafone acquire new assets in emerging countries like India, Turkey and Africa, while the deal should help Verizon Wireless improve its mobile portfolio.
Verizon Wireless and AT&T, which own a major share in the US wireless market, are facing competition from Sprint and T-Mobile USA.
The acquisition talks began a few weeks back and an agreement is expected in September.
According to reports, Verizon Wireless is said to have approached several banks to raise $60bn to fund the deal, while the rest of the stake could be paid through Verizon Communications shares.
Vodafone agreed to buy German cable firm Kabel Deutschland for €7.7bn in January 2013.
