The U.S. Justice Department has approved AT&T's purchase of Centennial Communications, and the deal will add about 1.1 million users to AT&T (NYSE: T)'s subscriber base.

The $944 million deal will mean AT&T's subscriber base will exceed 80 million subscribers, but it still trails Verizon Wireless. Centennial also has large holdings of spectrum in the Midwestern and Southeastern United States, which should boost AT&T's coverage and footprint. Centennial also is a licensee of the 850-MHz spectrum, which AT&T is using to improve its 3G coverage in major metropolitan areas.

The second-largest U.S. mobile operator will have to divest assets in southwestern Mississippi and central Louisiana because of competitive issues, and AT&T said it will sell some of these assets to Verizon. Asset deals among rivals are relatively common in mobile mergers, as Verizon recently sold assets to AT&T in order to complete its acquisition of Alltel.

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— Marin Perez, InformationWeek