Google will come out in mid-2008 with a mobile phone platform that incorporates a variety of Google online services and lets outside developers create applications, The Wall Street Journal reported Tuesday.

The goal is to make Google applications and services as easily accessible on mobile phones as PCs, so that the company can extend its advertising business to cell phones and other wireless devices. Google may announce its mobile platform within weeks, according to the Journal.

The Journal's article, based on anonymous sources, is the latest of multiple reports over the past six months or so about Google's plans for the mobile market.

Although at some point it was speculated that Google might be involved in the actual manufacturing of phone hardware, that rumor is now discredited, as Google is expected to focus on developing mobile software.

For Google, it's critical to replicate on mobile phones the success it has had on PC-based online advertising. After years of unfulfilled promises, mobile advertising will boom in coming years, as people spend more time using the Internet via their cell phones.

The Kelsey Group recently forecast that mobile search and display advertising in the U.S. will hit US$33.2 million this year and grow at a compound annual rate of 112 percent through 2012, when it will total US$1.4 billion.

Kelsey Group also expects the number of mobile Internet users to grow at a 20 percent compound annual clip in the U.S. through 2012, when there will be almost 92 million people going online via their cell phones.

Worldwide, mobile ad spending is expected to reach US$1.5 billion this year and grow to US$11.3 billion by 2011, according to market researcher Informa Telecoms & Media.

Google is far from alone in its interest at pursuing this emerging opportunity in the mobile market, where all major telecom, online publishing and Internet players are jockeying for position.

Of course, delivering online services and applications via mobile phones isn't as straightforward as doing it via PCs. In the mobile market, providers of online applications often have to strike up deals and partnerships with handset makers and wireless carriers.

In a recent interview with the IDG News Service, Marissa Mayer, Google's vice president of Search Products & User Experience, acknowledged there are specific challenges to bringing Google services to cell-phone subscribers.

"The mobile space is very complicated," she said.

Google has pursued various avenues for making its search engines and other services available via cell phones. It has adapted Google Web sites for mobile browsers, developed mobile applications people can download themselves, as well as preloaded Google software in handsets via formal partnerships with mobile industry players.