US mobile search advertising revenues are projected to reach $1.4 billion in 2012, up from $33.2 million in 2007, according to The Kelsey Group. The optimistic estimate represents a compound annual growth rate of 112%.

"Advertisers in the US are the most aggressive in terms of messaging to potential US consumers," said Matt Booth, senior vice president at Kelsey, in a statement. "Given the relatively high spend levels, we believe advertisers will continue to look into innovative solutions, including mobile, that demonstrate a clear ROI on ad spend."

Kelsey figured that ad-sponsored directory assistance would contribute to mobile search revenue. Mobile Internet ads on information sites such as Google Maps would contribute as well.

The estimates also included "multi-modal applications," which convert voice commands into data and information requests.

eMarketer's mobile search ad revenue estimate for 2011 is $713.7 million, up from the 2007 forecast of $13.5 million. The number focuses solely on money generated by ads.

"A $715 million mobile search market is not a foregone conclusion," said John du Pre Gauntt, eMarketer senior analyst, "but many of the behavioral factors are in place in the US market to push mobile search forward. For one, there is already a strong correlation between mobile Internet use and accessing mobile search services."

Mr. Gauntt said that the US mobile search market will suffer growing pains over the next two to three years as the tug of war between operators, portal players, media and mobile search start-ups continues for the title of mobile search leader.