Which is like sending out a challenge to hackers all over the world, inviting them to break iPhone out of its AT&T bondage and set it free for wannabe iPhoners the world over.

And there’s been plenty of attempts to do just that. Successful attempts.

In addition to iPhone’s AT&T ties, the device also uses GSM technology, and one of the features of GSM is its Subscriber Identity Module, otherwise known as a SIM card or chip. Because a SIM contains the user’s phone book, and other information, users can transfer data and software by switching or reprogramming SIMs.

Which is what hackers did last July, shortly after the iPhone’s debut. However, the hack wasn’t for the fainthearted. It required programming knowledge and special equipment.

Then there’s the iPHoneSIMfree.com gang, whose exploits have been chronicled on tech blog Engadget.com.

According to the blog, a six-man team from iPhoneSIMfree had been working nonstop since iPhone hit the marketplace and came up with a small piece of software enabling the device to work with other cell carriers. And, to prove it, the hackers demoed the software for the Engadget staff.

But around the same time the iPhoneSIMFree bunch were showing off their hi-tech chops, a teenager from Glen Rock, N.J., who, along with three online collaborators, came up with an iPhone hack of his own.

George Hotz, 17, spent his summer figuring out how to free the iPhone from AT&T. However, the “Hotz Hack” is complicated and requires both some programming expertise as well as some soldering iron handiwork. Even so, an Associated Press reporter confirmed that the hack did work, and personally witnessed Hotz place a SIM from the reporter’s phone into an iPhone, and then place calls on the reporter’s carrier – T-Mobile.

But are the hacks legal? Maybe. If you hack your own iPhone for personal use on a different carrier, you probably won’t attract much attention, except, of course, the envy of your friends.

But hacking for financial gain – that’s another matter.

For example, one Northern Ireland company claiming to possess a hack – Uniquephones.com – says they’re ready to go to market, but are now rethinking their position after an international law firm representing AT&T told them the software contained material copyrighted by Apple.

Meanwhile, George Hotz’s hard work has paid off for the teenager. He recently accepted a consulting position with CertiCell, a Louisville, Ky.-based mobile phone company, and posted on his blog that he traded his hacked iPhone for “a sweet Nissan 350Z and 3 8GB iPhones.”

“This has been a great end to a great summer,” Hotz wrote on his blog.