Their biggest obstacle isn't each other. It's wireless carriers such as AT&T Inc and Verizon Wireless which have kept mobile Internet rates high while defending other revenue sources that the advertising may undermine, Bloomberg News reported.

At stake is a market that may surge 10-fold to 16.2 billion U.S. dollars globally by 2011, says EMarketer Inc, a research firm in New York. Google, based in Mountain View, California, sees as much as half of future sales coming from mobile phones. While the US accounts for about 50 percent of global revenue from promotions viewed on computers, the figure drops to 27 percent on phones and may rise to 29 percent by 2011.

"The carriers are too busy trying to protect the money they are making now to look at the next way to make money," said Chad Stoller, who heads the mobile practice at Organic, a San Francisco ad agency. Phone companies "want to control every aspect of the relationship between the consumer and the phone."

Even though they would share in the revenue, US phone companies have not yet embraced ads because they are wary of giving up control of their networks, ad buyers and Internet companies say.

The top US wireless companies boost earnings by selling add-ons like ring tones and Web access. They don't offer cheap all-you-can-eat Internet plans, meaning just 13 percent of US subscribers surfed the Web on phones last quarter, said Nielsen Co in New York. More than half of Japan's mobile users access the Web, according to Tokyo's Video Research Interactive Inc.

And there are so many different networks, phones and programs that it's tough to create ads in the US.

Google, Microsoft and Yahoo want to sell ads that appear as banners on mobile Web pages, link to on-the-go Internet searches, promote nearby attractions on driving directions and send coupons for products via text messages. Phone-service providers would get a cut of ad sales in exchange for participation.

Telecommunication companies worry that ad-funded Internet and phone services may jeopardize revenue from subscriptions, said Phil Asmundson, a vice chairman at Deloitte & Touche LLP in Stamford, Connecticut. Cheap Web access would make it easier for consumers to go directly to Google, bypassing the carriers' pages and services such as searches, driving directions and videos.

Google, the most popular Web search company, aims to generate half its revenue from mobile phones within 10 years, up from almost none today. Microsoft wants a revenue source outside of personal computer programs. Mobile subscribers will outnumber PC users by three to one by 2008, says Credit Suisse Group.