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.