Armed with a soldering iron and a large supply of energy drinks, a slight, curly haired teenager has developed a way to make the iPhone, arguably the gadget of the year, available to a much wider audience.

George Hotz of Glen Rock, N.J., spent his last summer before college figuring out how to "unlock" the iPhone, freeing it from being restricted to a single carrier, AT&T Inc.

The procedure, which the 17-year-old laid out on his blog Thursday, raises the possibility of a cottage industry springing up to buy iPhones, unlocking them and then selling them to people who don't want AT&T service or can't get it, particularly overseas.

The phone, which combines an innovative touch-screen interface with the media-playing abilities of the iPod, is currently sold only in the U.S.

In a video post, Hotz demonstrated an iPhone running on T-Mobile's network, the only major U.S. carrier apart from AT&T that is compatible with the iPhone's cellular technology.

The hack is complicated and requires skill with both soldering and software, and missteps may result in the iPhone becoming useless, so it's unlikely to become a household procedure.

"But that's the simplest I could make them," Hotz said in a phone interview. The next step, he said, would be for someone to develop a way to unlock the phone using only software.

AT&T Inc. spokesman Mark Siegel and Apple spokeswoman Jennifer Bowcock said their companies had no comment. Hotz said the companies had not been in touch with him.

Apple shares rose $4.23, or 3.2 percent, to close at $135.30 on Friday. AT&T shares gained 26 cents, or 0.7 percent, to close at $40.36.

The iPhone has already been made to work on overseas networks using another method, which involves copying information from the Subscriber Identity Module, a small card with a chip that identifies a subscriber to the cell-phone network.

The SIM-chip method does not involve any soldering, but does require special equipment, and it doesn't unlock the phone — each new SIM chip has to be reprogrammed for use on a particular iPhone.

Both hacks leave intact the iPhone's many functions, including a built-in camera and the ability to access Wi-Fi networks. The only thing that won't work is the "visual voicemail" feature, which lists voice messages as if they were incoming e-mail.

Since the details of both hacks are public, Apple may be able to modify the iPhone production line to make new phones invulnerable. The company has said it plans to introduce the phone in Europe this year, but it hasn't set a date or identified carriers.

There is apparently no U.S. law against unlocking cell phones. Last year, the Library of Congress specifically excluded cell-phone unlocking from coverage under the Digital Millennium Copyright Act. Among other things, the law has been used to prosecute people who modify game consoles to play a wider variety of games.

Hotz collaborated online with four other people, two of them in Russia, to develop the unlocking process.

"Then there are two guys who I think are somewhere U.S.-side," Hotz said. He knows them only by their online handles.

Hotz himself spent about 500 hours on the project since the iPhone went on sale. On Thursday, he put the unlocked iPhone up for sale on eBay, where the high bid was above $3,000 on Friday afternoon. The model, with 4 gigabytes of memory, sells for $499 new.

"Some of my friends think I wasted my summer but I think it was worth it," he told The Record of Bergen County, which reported Hotz's hack Friday.

Hotz heads for college on Saturday. He plans to major in neuroscience — or "hacking the brain!" as he put it to the newspaper — at the Rochester Institute of Technology.