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

A statement issued by the company said that installing one of the widely available 'unlocking' programs would "likely" result in the phone becoming "permanently inoperable" when future software updates were released.

The next iPhone software update was due out 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 claiming to have unlocked it, and internet companies have begun selling software which allows the device to be used on networks other than Apple's chosen carriers, which include AT&T in America and O2 in the UK.

For as little £25, and in some cases free of charge, owners can buy a piece of software which, once installed, allows them to insert their existing Sim into the iPhone and avoid signing a minimum 18-month contract costing £35 a month.

The unlock means that UK residents not content to wait until the device's official launch on November 9 can buy the iPhone from an Apple store in America and begin using it here beforehand.

Apple stressed that it was not setting out deliberately to counteract the effects of such programs with its updates but at a recent event in London, the company's chief executive, Steve Jobs, 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, iPhoneSIMfree.com, has said that it cannot guarantee its software is 'update resistant'.

Another - 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 on its website. "We strongly believe that it will work without any modifications due to the nature of our update."

Philip W Schiller, Apple’s senior vice president for worldwide product marketing, said it was unfortunate that some unlocking programs had caused damage to the iPhone software, but stressed that Apple could not responsible for any such consequences.

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