Ingenio, the pay-per-call technology service that was powering the call/search ads for AOL, (NYSE: TWX) Marchex, Miva and others, has been bought out by AT&T. Financial details were not disclosed, and the transaction is expected to close in early January 2008. The company’s platform allows provisioning unique published phone numbers to track calls to businesses generated by those ads (contextual or otherwise), and advertisers’ fees are based on the volume of these leads.

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San Francisco, CA-based Ingenio was founded in 1999, and had investment from Benchmark Capital, along with the Carlyle Group. It had done four main funding rounds since it was formed in 1999, raising a total of $109 million. According to this story from last year, Ingenio had revenues of $83 million in 2005, and had been profitable for last three years.

AT&T (NYSE: T) plans to integrate Ingenio’s ad platform into its directory service and local search advertising portfolio, including the Yellowpages.com network, AT&T Real Yellow Pages and 1-800-Yellow Pages. It expects to retain Ingenio’s management team, but the division will be headed by Charles Stubbs, president and CEO of Yellowpages.com. Besides the online technology, Ingenio also recently expanded its mobile search products with a new app for iPhone users, as well as a downloadable local search application that is currently available on 20 AT&T handsets.

More details in release.