Apple has warned iPhone owners that they could cause “irreparable" damage to the device if they try to make it work on an unauthorised network.

The company said that installing the widely available “unlocking” software was likely to result in the phone becoming “permanently inoperable” when future updates are released.

The next iPhone software update is due later this week, Apple said, adding that any “permanent inability” to use the device as a result of installing unlocking software was not covered under warranty.

Since the phone was released, a number of hackers have come forward having unlocked it. Internet companies have begun selling software that allows the device to be used on networks other than Apple’s chosen carriers, which include AT&T in America and O2 in Britain.

For as little £25, and in some cases for nothing, owners can obtain a piece of software that allows them to insert their existing SIM card into the iPhone and avoid signing a minimum 18-month contract costing as much as £55 a month.

Unlocking the device would allow UK residents who cannot wait until the device’s official launch on November 9 to buy the iPhone from an Apple store in America and begin using it here beforehand.

Apple stressed that it was not setting out to deliberately counteract the effects of such programs with its updates. But at a recent event in London, Steve Jobs, the company’s chief executive, suggested he was not concerned about the impact of unlocking programs. The firm was in a game of cat and mouse" with the hackers, he said.

One unlocking service, iPhoneSIM-free.com, has said that it cannot guarantee its software is “update resistant”.

Another site, iPhone Unlock UK, warned owners to refuse updates until it had confirmed that they were compatible with its service.

“There have been many ‘scare stories’ regarding the impending iPhone firmware update, and that it will break unlocked phones,” iPhone Unlock UK said. “We strongly believe that it will work without any modifications”.

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