A hacker group released a free, open source unlock for Apple's iPhone late Tuesday, just a day after a commercial company started selling something similar for as much as $99 through a network of online resellers.

The iPhone Dev Team, a dozen programmers who began their attempts to break the iPhone's reliance on AT&T in early July, have posted their hack on download servers. According to several sites, including Gizmodo and Engadget, the iPhone Dev Team unlock exploits the same iPhone bug as the for-money iPhoneSIMFree hack to do its magic. The two groups, however, came up with their solutions independently.

But the process isn't for the faint of heart. "This unlock is not for everybody!" the iPhone Dev Team warned. The procedure involves several separate programs -- some of which must be obtained elsewhere on the Internet -- and requires that iPhone owners execute commands from a shell screen on the Mac or PC.

Even so, reports have been posted to the team's site from users in more than 40 countries that the unlock hack works, and after a swap of the iPhone's included SIM card with one from another cellular service provider, that they've been able to access more than 90 different carriers. The iPhone's distinctive Visual Voicemail, which lets users select voice-mail messages rather than listen to them in the order they were received, is missing after an unlock; that feature relies on AT&T's back end. Some users have also reported that the iPhone's connection to YouTube no longer works after the hack is applied.

The iPhone Dev Team is already working on a one-click tool sporting a graphical interface that will unlock an iPhone, but it had not been released as of this morning. "A new version of the GUI tool is almost complete," the group said on its site.

It's likely, however, that any unlock will be undone by the next iPhone update, which Apple has said will be issued sometime this month to give the device new capabilities, such as Wi-Fi downloading from iTunes. The iPhoneSIMFree group, for example, has hammered the caveat into potential buyers' heads:

"We cannot offer any guarantee should Apple Inc. choose to re-lock the phone after a future update," it stated in a FAQ.

Resellers of the iPhoneSIMFree hack, who have priced the unlock as low as $45, have repeated the no-guarantee mantra.

Apple has repeatedly refused to comment on the various iPhone unlock hacks -- paid versions or free ones.