Bidding on what may be the last large pieces of wireless spectrum to be auctioned off by the Federal Communications Commission exceeded $15 billion on Thursday, well above the $10 billion target set before the sale began.

In a win for wireless "open access" advocates, bidding for the highly desirable "C block" of spectrum topped the F.C.C.'s $4.6 billion reserve price. That suggests that some bidder has provisionally won the frequencies.

C block, a 22-megahertz chunk of spectrum, is unique in that the winning bidder will have to let its customers use any cell phone or wireless device, not just the hardware sold by the company offering the service, as is now the case.

F.C.C. chairman Kevin Martin called this so-called open-access provision "an important transformation for the wireless industry."

While this open access might make the frequencies less attractive to some bidders, it is believed to make them more attractive to companies like Google that have expressed interest in offering wireless services without getting into the business of selling hardware at retail stores.

Whether Google was the high bidder, as some suspect, will not be known until the auction of all the available lots of spectrum ends. Auction rules require anonymity until there are no more bids for any of the licenses on the block, and bidding continues on the smaller regional licenses, so the winner of the C block may not be announced for weeks.

Google has made it clear that it would meet the reserve price for the C block; if Google is the high bidder and wins, the company will instantly become a formidable player in the wireless industry.

Verizon Wireless, AT&T, and Echostar are among those also thought to be interested in the C block.

Some have suggested that Google was "bidding to lose" the auction because it had already won the two open-access provisions, and because of the cost of building an actual network—as much as $25 billion.

Art Brosky of Public Knowledge, a public-interest group focused on digital communication, said that if Google won the C block, it could partner with an existing provider—Sprint would be a good candidate—and modify that provider's network to make it compatible with the C block. "Then we could have a true open network," Brodsky said.

Open access advocates praised today's developments. The Public Interest Spectrum Coalition, a consortium of consumer groups, said, "The fact that bidders met the $4.6 billion threshold is a welcome development for consumers."

"We hope that the freedom that will develop as the new spectrum opens up will carry over into the existing cellular network," it added.