The Google phone returned to the rumor mill today after the Wall Street Journal reported that the search giant has approached a number of wireless phone operators and handset makers, as it looks for a piece of the market for advertisements on cell phones to complement the huge ad business it has already built online.

According to the report, which cites unnamed sources "familiar with the plans", Google has developed prototype handsets, made propositions to operators such as T-Mobile USA and Verizon Wireless, and talked over technical specifications with phone manufacturers, hoping to get them to make devices based on its specs and that multiple carriers will offer them.

Google is in for a challenge though, as wireless carriers will be wary about losing control over the mobile-ad market. Moreover, it doesn't help that Google is stepping into the carrier's turf by pushing the open access issue with the FCC for the 700MHz wireless spectrum auction.

The company's past efforts to get its software on cellphones includes deals with LG and Apple. The long-rumored Google phones are reportedly still in the planning stages and wouldn't be available to consumers until next year at the earliest.