The U.S Federal Trade Commission signed off on Google's purchase of AdMob, a mobile ad display company, clearing the way for the company to extend its advertising empire into the burgeoning smart phone market. Mobile ad spending worldwide increased 74 percent last year, to $913.5 million, Entrepreneur magazine reported earlier this year.

In a strange way, Apple's ambitions in the mobile ad space -- under the cute name, "iAd" -- helped Google. The FTC was nervous that the AdMob deal would create a monopoly. The entrance of Apple, whose iPhone still outsells Google's Android phones worldwide, creates competition, or at least the specter of competition:

The commission, on a 5-0 vote, said its decision was a difficult one, but said recent market developments, particularly actions by Apple Inc. (AAPL), "should mitigate the anticompetitive effects of Google's AdMob acquisition."

The next phase of the cold war between these two companies might be in patents. Google has secured a location-based advertising patent. If the mobile ad war is anything like the mobile phone war, expect the patent battle to be bloody and protracted.

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