And Google executives have made it plain that they view the mobile market as the future of advertising. CEO Eric Schmidt said in October that much of the company’s development and acquisition money would be going into the mobile market.

“That’s why we’re basically pushing our rate of hiring, partnerships with wireless and developers, but also we’re going to focus more on strategic deals and acquisitions as we’ve discussed publicly. We’re open for business in making strategic acquisitions both large and small,” Schmidt said. It’s not clear whether a $750 million stock deal, such as the AdMob purchase, counts as large or small. It’s about half of what Google paid for YouTube, and Google paid $3.1 billion for advertising network provider DoubleClick, Google’s largest acquisition.

It could well be worth the price. AdMob’s growth has corresponded to the popularity of such devices as the iPhone and Research In Motion’s Blackberry. And Google, of course, has its own smartphone operating system, Android. That operating system is getting its most high-profile test with the Droid mobile phone made by Motorola and carried on the Verizon Wireless network. The Droid launched last week.

A group of Morgan Stanley analysts led by tech guru Mary Meeker writes in their latest report on Google: “With Google’s free and highly customizable policy for Android, we could see multitudes of Android-based devices (smartphones, feature phones, media players, netbooks), and we would not be surprised to see Android’s usage share (and Google’s monetization opportunities from associated services) continue to rise further.” Meeker expects shipments of mobile devices to outpace personal computer shipments by 2012.

Sanford C. Bernstein & Co. expects the U.S. mobile advertising market to reach $2 billion to $3 billion by 2013, Bloomberg reports. The market is less than $1 billion now.

“It’s right in the area where Google is looking for growth,” Jeffrey Lindsay, a Bernstein analyst, told Bloomberg. “It’s probably a great acquisition for them.”