Microsoft has won U.S. antitrust approval to buy the Internet phone service Skype, the Federal Trade Commission said in a website posting on Friday.

Microsoft announced in May it was buying Skype for $8.5 billion, its biggest-ever acquisition, placing a rich bet on mobile and the Internet to try and best rivals such as Google Inc.

The approval was announced in a listing of deal approvals that comes out several times a week.

Microsoft's interest in the money-losing, but popular service highlights a need to gain new customers for its Windows and Office software. Skype has 145 million users on average each month and has gained favor among small businesses.

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