WASHINGTON (CNN) - The Justice Department Monday announced it has reached an agreement that allows Cingular Wireless to acquire AT&T Wireless in a $41 billion merger deal.

The approval by antitrust regulators requires Cingular to divest assets in 13 markets in 11 states, where the deal would result in higher prices for mobile-phone users, the Justice Department said.

The agreement was filed in U.S. District Court in Washington, along with a lawsuit that would block the transaction if the divestitures are not made.

When completed, the combined company will become the largest wireless telephone service in the United States.

"Today's action by the department ensures that consumers of mobile wireless services will continue to benefit from competition," said R. Hewitt Pate, assistant attorney general in charge of the Antitrust Division.

"Without these divestitures, wireless customers in these markets would have had fewer choices for their wireless telephone service and would have faced the risk of higher prices, lower quality service, and fewer choices for the newest high-speed mobile wireless data services," Pate said.

The required Cingular divestitures are in Connecticut, Georgia, Kansas, Kentucky, Louisiana, Massachusetts, Missouri, Michigan, Oklahoma, Tennessee and Texas.

Final Federal Communications Commission (FCC) approval is expected, because the FCC has been coordinating closely with the Justice Department throughout the antitrust analysis.

Cingular, headquartered in Atlanta, is the nation's second-largest provider of mobile wireless services, with 24 million subscribers. AT&T Wireless (up $0.12 to $14.92, Research), the third-largest wireless provider, is headquartered in Redmond, Wash., and has 22 million subscribers.

Together, the combined provider will top the current number one service provider in the industry, Verizon Wireless (Research), which has 37 million subscribers.  

From CNN Producer Terry Frieden