A recent study of Search 2.0 trends by DoubleClick Performics claims that mobile display and search are still in their infancy.

Though projected to grow more than 400 percent to $4.78 billion by 2011, mobile advertising will account for only 10 percent of the total online spend at that time.

An estimated 23 million mobile search users live in the United States, reflecting nearly 9 percent of the mobile subscriber population and 75 percent of mobile Internet users.

While fewer in number, mobile searchers look like the larger mobile Internet user population of which they are a subset: most are male and in the 18-44 age group, according to DoubleClick Performics, whose DoubleClick parent is now owned by Google Inc.

Devices matter for mobile search. Users who own smartphones with QWERTY keypads and larger screens are more than three times as likely to access the Web and nearly four times as likely to search as users with other types of phones.

Research shows that the U.S. mobile searcher prefers task-oriented content such as maps, weather, local information and news over entertainment and sports.

DoubleClick Performics recommends that mobile ad messaging must be shorter and should feature carrier and markup language targeting.

"Advertisers should understand that 84 percent of mobile searchers expect sites they frequent to have a dedicated mobile version," the report said.

"At the most basic and obvious level this means linking to a mobile Web site or using click-to-call. Advertisers must add value by supporting the fundamental utility of easy access to immediately actionable information. Mobile searchers want answers, not links."

There are currently three mobile search consumer tools: linking to a mobile Web site, click-to-call and click-to-buy shopping comparison.

But the existing mobile ecosystem offers a less than satisfying mobile search experience, DoubleClick Performics said.

For example, mainstream search engines, while focused short-term on building local mobile listings, offer mobile Web users access to the Internet through non-mobile search.

Even though users prefer going off-deck to access the entire Web, navigation is cumbersome and most sites are not optimized for mobile viewing, DoubleClick Performics said.

New types of mobile content will be slower to market since publishers and other content developers must create their own .mobi or WAP-enabled sites.

To meet users' expectations for the full Internet experience, search engines may convince marketers in specific categories to adapt their sites for mobile devices to keep pace with consumer demand, the report said.

Mobile search players cited in the report include carrier 411, Goog 411, MSN/Tell Me and Yahoo oneSearch. All players offer SMS and Web search, relying heavily on access to local databases and directories.

"[Marketers] should mobilize their Web sites and they should localize their product data," said Cam Balzer, vice president of emerging media at DoubleClick Performics and author of the report.

"The key thing we're seeing is that marketers are interested in buying clicks on sites," he said. "The first question we ask is, 'Where do you want the clicks to go?' and most of them don't have viable mobile e-commerce sites.

"The second thing, and the biggest challenge, is localizing product data. Local empowerment of mobile data is where there's going to be significant traction."