Programmers who wrote free software that unlocks Apple's iPhone have disputed the company's claim that their hacks can damage the device and promised to battle any attempt by Apple to "brick" modified phones.

In a message posted to the iPhone forum on the Hackint0sh Web site, someone claiming to represent the iPhone Dev Team said the group would answer the firmware update expected this week with a tool of its own that would return any unlocked phone to a factory-fresh condition. That will prevent the iPhone from being "bricked", or incapacitated, when the update is applied.

"We will provide you with a tool in the next week which will be able to recover your 'nck' counter and 'seczones' and even enable you to restore your phone to a factory-like state if you are really [determined] to update your phone," said someone identified as "sam."

He also said the iPhone Dev Team took exception with Apple's contention that modifications could break the device. "[Apple speaks] of 'damage' done to the firmware and 'unauthorised access' to our own property," the message said.

"[But] Apple [has] now announced [that] the next firmware update, [which] we may expect later this week, will possibly break the handsets of all of us free users in the world intentionally."

The message went on to say, of Apple's claims, "we know better" and that the unlocking software was "not causing 'damage' as they want to make us believe".

The iPhone Dev Team is responsible for creating anySIM, a free open-source utility that lets users make and receive calls on networks other than that of AT&T, the only US authorised carrier for the iPhone. The anySIM software is one of several unlocking hacks now in circulation.

The hackers' manifesto is the latest in what Apple CEO Steve Jobs called a "cat-and-mouse game" between his company and those who want to make unauthorised changes to the iPhone. In London a week ago to tout the smart phone's November 9 UK launch, Jobs implied that Apple would counter attempts to unlock the iPhone.

"People will try to break in, and it's our job to stop them breaking in," he said.

Apple has also issued a statement saying that any modification to an iPhone automatically voids its warranty. It also warned customers against unlocking their phones. "Apple has discovered that many of the unauthorised iPhone unlocking programs ... will likely result in the modified iPhone becoming permanently inoperable when a future Apple-supplied iPhone software update is installed," the company said.

A firmware update, the third since the iPhone went on sale in late June, will be released through iTunes. Apple is expected to add new features to the phone, including the ability to purchase music over a Wi-Fi connection.

The iPhone Dev Team spokesman advised users who had already unlocked their phones to not apply the update, saying they should instead wait while others, presumably including the iPhone Dev Team's own programmers, analysed it.

The spokesman claimed that about 500,000 copies of the free unlocking tool had been downloaded. If true, that would mean that almost half of the iPhones sold so far had been unlocked. Apple only two weeks ago said it had sold its millionth iPhone.