Cellphone Showdown: In this Corner, the GPhone

Sam Gustin observes: It's been awhile since Google played the role of the underdog. Nevertheless, it would be folly to underestimate the tech titan.

Now that the Federal Communications Commission has approved HTC's "Dream" handset -- expected to be the first mobile phone to feature Google's "Android" operating system -- the stage is being set for a four-way showdown for dominance in the mobile phone market.

The combatants: Apple's iPhone, which has proved to be one of the most popular mobile devices ever launched; Research in Motion's BlackBerry, which still leads the corporate and enterprise market; and Palm, which is showing early signs of a mini-resurgence thanks to its well-received Centro device and early buzz over its Treo Pro model.

And finally, the newcomer: HTC's "Dream," featuring the Android OS, which will be sold by T-Mobile. Today, Google released an updated software developer kit (SDK) for Android, which will allow programmers to create new applications for the operating system, much as Apple as done with the iPhone.

But make no mistake: The HTC/Google "Dream" is definitely the underdog, and faces a monumental challenge going up against the iPhone and the BlackBerry. Nevertheless, the device's impending arrival means the cellphone battle has been joined.

For Google, Android could be a promising revenue source as the company seeks to diversify from its core business of web search advertising. The company has made no secret of its view that the mobile advertising space could be a goldmine for the company.

 "We can make more money on mobile than we do on the desktop, eventually," Google chief executive Eric Schmidt told CNBC recently. That's quite a statement considering the billions of dollars the company currently rakes in from its desktop search ad business.

Google is hoping to serve targeted advertising to users based on their interests and geographical location -- something the company seems will positioned to do thanks to its Google Local Search service.

HTC's Android-powered "Dream" is expected to hit stores by November 10th, right in time for the holiday shopping season.