We’ve all heard the projections: mobile is going to be big. Really, really big.

With an estimated 240 million wireless subscribers in the U.S., mobile is already a $350 billion sector. Of those millions of subscribers, 70 percent now send or receive text messages, 32 million use their phones to go online and 41 percent use their wireless devices to send photos, according to numbers from Nielsen Mobile (formerly Telephia).

And the mobile ad market? eMarketer predicts it will skyrocket by 2011 — up to $3.6 billion from $123.8 million in 2006.

If their actions are any indication, the leaders in the internet space seem to agree. The major names in the web have been pouncing on mobile startups and forming massive partnership with wireless carriers across the globe. But to make eMarketer’s predictions a reality, there’s a whole lot of innovating and upgrading that needs to take place over the next four years.

In Europe, for example, where new mobile technologies are adapted more quickly, only 23 percent of wireless consumers have adopted third-generation wireless devices. So-called 3G phones incorporate more advanced and faster technologies that are able to deliver content, and thus ads, more rapidly and effectively. In the U.S., however, the number of consumers with 3G phones is significantly lower.

The lingering question for interactive marketers with an interest in the wireless space seems to be: where to start?

One way to begin is to take a closer look at the mobile models being adopted by the traditional web players in the wireless space. Let’s take a look at how Google, Yahoo! and AOL are shaping their mobile plays.

Author notes: Leah Messinger is a freelance writer. Read full bio.

As is its custom, Google has for several years been quietly — some might even say secretively — building up the infrastructure to support its apparently vast mobile plans. Since the start of the millennium, Google has been purchasing dark fiber (also known as unlit optical fiber), laid in preparation for the internet boom but as-of-yet unused by the telcos. Earlier this year, iMedia wrote about the potential for Google to light its dark fiber and lower transmission costs, especially to Asia.

In addition to dark fiber, Google announced in July that it intends to bid in a January 2008 auction for licenses for the 700 MHz electromagnetic spectrum controlled by the Federal Communications Commission. Broadcasters now use that spectrum for television, but it’s likely Google will want to use it for broadband communications to establish an open wireless broadband network. The Mountain View, Calif.-based search giant may also bid on the 900 and 1800 MHz spectrum in the U.K.

In case you were thinking Google may have started to relax a bit after a busy summer, well, September was another busy month for the company. That’s when Google announced it had extended its AdSense contextual text and image advertising program to mobile. The mobile version of AdSense is designed for users who have optimized versions of their websites for easy navigation on wireless devices. (That’s only 8 percent of the websites for the top 1,000 U.S. brands, according to an eMarketer study.) Mobile AdSense is now available in the U.S., England, Italy, France, Germany, Spain, Ireland, Russia, Netherlands, Australia, India, China and Japan.

Later in September, Google revealed it had acquired Boston-based startup Zingku. Still in private beta, Zingku lets users share content among themselves and between the desktop and mobile devices. The company also has a program for merchants interested in distributing mobile-specific flyers to announce new products or upcoming events.

And just last month, in a display of appreciation for consonance following the Zingku purchase, Google announced the acquisition of Jaiku, a Finnish Twitter wannabe. Jaiku is a free service that lets users follow their friends’ activities in real time.

There’s also the Gphone, long-rumored to emerge as an iPhone competitor. Recent reports from PC World and The New York Times, however, suggest that the Gphone won’t be an actual device but rather an open source mobile operating system set to challenge Microsoft’s dominance in the mobile space with its Windows Mobile operating system. If the new crop of rumors proves correct, Google might just shake up the entire mobile market by softening the longstanding grip on the industry by the wireless carriers.

As has become custom, it seems that with both its infrastructural developments and its incremental software acquisitions, Google has positioned itself for mobile dominance.

Tired of playing second search engine to Google, Yahoo recently announced its own big mobile play. In early October, the San Francisco-based web giant announced a partnership with Spanish telecom Telefonica to make Yahoo’s mobile oneSearch the primary search service for Telefonica customers in 15 countries in Europe and Latin America. The agreement sets up Yahoo to reach a potential 100 million consumers via Yahoo mail and Flickr, in addition to oneSearch.

Yahoo also reached a similar arrangement with six wireless providers in Asia earlier this year to provide oneSearch services in the Pacific Rim.

OneSearch is Yahoo’s main mobile search tool, providing location-based results for services plus news and financial information. In early September, Yahoo partnered its oneSearch tool with ELLE to offer search and marketing services related to New York Fashion Week. The partnership will also extend to subsequent fashion weeks in Italy and France.

Earlier this year, Yahoo also launched services for mobile publishers in 19 countries in Latin America, North America, Europe, Asia and the U.K. Its Mobile Ad Ne
twork, launched with MobiTV, Opera and go2, allows publishers to choose a variety of ad formats, including display, sponsored links, video or in-game.

There’s no chatter yet as to whether Yahoo holds the same aspirations as Google to acquire hardware or build powerful software with the potential to re-write the wireless industry’s old, reliable script, but the company is certainly making serious moves in the mobile realm.

With its 2000 launch of AIM for mobile, AOL was one of the earliest portal companies to enter the wireless space.

For the next few years, however, the company seemed to go a bit off track as it pursued the B2B mobile market. That’s when, in the early 2000s, AOL acquired mobile software company Tegic Communications and mobile operating system company Wildseed. After a strategic review earlier this year, Time Warner-owned AOL decided to sell off those companies and refocus its gaze on the consumer market.

Since then, AOL has made its Cityguide, Moviefone, Mapquest, AOL Mail and search products available via mobile. In a nutshell, the company’s mobile strategy consists of making its popular desktop features available and user friendly for mobile consumers, says AOL Mobile spokesperson Scott Falconer.

Falconer says AOL has established relationships with all of the major U.S. wireless carriers, as well as several international telcos, and is working with device manufacturers to provide consumer phones with pre-loaded AOL tools. These latter partnerships may prove especially valuable as AOL makes more of a media play in mobile as it develops its Winamp music and BlueString photo products for wireless use.

AOL’s most important move in the mobile space to date may be its acquisition of Third Screen Media, a software and services company that enables mobile advertising and will provide an additional — and likely significant — revenue stream for the company.

Despite Google, Yahoo and AOL’s headlong rush into the mobile market, many interactive marketers have been slow to follow. eMarketer reports that as of last December, only 13 percent of interactive marketers made use of text messaging and only 11 percent advertised via WAP sites.

This disparity in mobile investments between the web leaders and advertisers highlights the discomfort of many interactive marketers to try out this relatively new space.

Of course, there is danger in entering a new market unprepared — a lack of familiarity with various mobile technologies and platforms can feel overwhelming for marketers who might otherwise be game to try new approaches. But jumping into the market too late holds its own risks.

The fact remains that key demographic groups are moving heavily into mobile and cutting down on their desktop web time. For marketers, that means it’s time to move with them.

One relatively painless point of entry for marketers is to make sure each client develops a mobile-compatible version of its traditional website, and when the client is ready to embark on a mobile campaign, the supporting infrastructure will already be in place.

Only then should you decide where you want to target your mobile marketing efforts. With its online track record and seemingly holistic approach to the mobile space, Google seems a logical choice. Its standard AdSense platform has more than proven itself online, so taking up the company’s mobile offerings seems to offer maximum gain with minimum risk.

But that doesn’t mean it’s time to overlook Yahoo and AOL. Though AOL’s mobile play seems almost haphazard, along the lines of an afterthought even, numbers from Hitwise suggest AOL is having some of the market’s most significant mobile success. Hitwise reports that AOL’s mobile web traffic is currently higher than Google’s and double that of MSN Mobile.

In other words, at least for now, AOL’s mobile tools are drawing more users for longer periods of time than Google.

The new question for interactive marketers then is: for how long?