Apple said on Monday that programs available on the Internet that allow the iPhone to be used with other service providers besides AT&T's Cingular network can irreparably damage the device. Apple said once an Apple-supplied software update is installed on the iPhone, it "will likely result in the modified iPhone becoming permanently inoperable."

"We are not doing anything proactively to disable iPhones that have been hacked or unlocked," Phil Schiller, Apple's head of worldwide product marking said in an interview with Reuters.

Asked how widespread the practice of downloading unlocking software, he replied, "We do not know."

Apple also said an iPhone that fails to work because of the installation of the unlocking software is not covered under the warranty.

Apple plans to release the next iPhone software update later this week, the company said in a statement. In the United States, AT&T Inc is the only authorized service provider for the iPhone.

"Apple strongly discourages users from installing unauthorized unlocking programs on their iPhones," the company said.

There are a number of unlocking software programs on the Internet, and, at least two of them, iUnlock and Anysim, can cause the iPhone to stop working once its software is updated.

Apple sharply cut the price of the iPhone earlier this month and revamped its full iPod line, adding a model that can browse the Web and buy songs wirelessly.

In the past few weeks, Apple and telecommunications service providers in Europe have been announcing deals to provide service for the iPhone.