TECHNOLOGY - A Google phone is the talk of the blogosphere - Rumors are rife that a possible iPhone killer is coming by next year.

The Google Phone is like the Roswell UFO: Few outsiders know if it really exists, but it's got a cult following.

Just months after iPhone mania gripped Silicon Valley gadget heads, suspense is building over reports that Google Inc. plans to release its own cellphone.

The blogosphere is buzzing with rumors that the search giant may announce Linux-based mobile software as early as this week and a Google phone, which observers have cheekily dubbed the GPhone, by early next year.

The latter is the most tantalizing to Silicon Valley, which is just getting over the June 29 launch of Apple Inc.'s multipurpose iPhone.

No one has displayed indisputable proof that the GPhone exists. But one thing is certain: Google, which took in nearly $11 billion last year from Web advertising, is investing heavily to target the potentially lucrative and hotly contested mobile search market.

The vision: mobile-phone service offered free of monthly charges to consumers willing to put up with advertising.

The goal: for Google to broker advertising on mobile phones the way it has on the Web.

The fear: Wireless carriers worry that Google will muscle its way into the young market and capture their wireless advertising dollars.

The official line: "Google doesn't comment on rumor or speculation," company spokeswoman Erin Fors said.

In recent months the Mountain View, Calif.-based company is rumored to have aggressively sought to partner with mobile carriers and manufacturers to make its search engine, maps program and other software available on more mobile handsets and networks.

If Google does make an even more forceful move with Google-branded handsets to be offered by multiple wireless carriers, it would mark a seismic shift in the mobile industry.

"For Google, maintaining itself as a search leader as wireless Internet access grows is extremely important since this is one area with extremely high growth prospects," said Weston Henderek, senior analyst with market research firm Current Analysis Inc.

At stake is the mobile-phone advertising dollar, object of an intensifying battle.

Research firm Frost & Sullivan in July estimated that the U.S. mobile advertising market would hit $450 million in 2007 and exceed $2 billion by 2011. Another firm, Gartner Inc., is even more bullish, predicting $3.9 billion in North America and $14.7 billion worldwide by 2011.