IPhone owners who have unlocked their handsets so they can use carriers other than AT&T Inc. may end up with a phone that doesn't work after the company's next software update, Apple Inc. warned Monday.

Since the iPhone debuted in June, hackers have posted a number of methods online to make it possible to use the iPhone on cellular networks other than AT&T, which is the exclusive official U.S. carrier for the iPhone.

Apple executives say they have discovered that many of those unauthorized unlocking programs cause some software damage to iPhones.

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Now, a software update that Apple plans to issue later this week that will add features such as accessibility to the iTunes Wi-Fi Music Store may end up making the touch-screen cell phone completely inoperable if it has been hacked into.

"This has nothing to do with proactively disabling a phone that is unlocked or hacked," Phil Schiller, Apple's senior vice president of worldwide product marketing, said in an interview. "It's unfortunate that some of these programs have caused damage to the iPhone software, but Apple cannot be responsible for ... those consequences."

Schiller said he didn't know how many iPhones are operating on different carriers.

The programs — including several that can be downloaded for free, and at least one that costs $25 — appear to be particularly popular with consumers in Europe.

Many Europeans have bought iPhones in the United States, but Apple will not be selling them or providing service for them in Europe until November.

"From the consumer point of view, this is extremely concerning to anyone who has unlocked their phone — especially people outside the U.S., where this is the only way to use the iPhone with any carrier," said Erica Sadun, a Denver computer programmer who developed a graphic interface for one software program that unlocks the iPhone. "Apple has essentially told them, 'Sorry, we cannot work with you.'"

John McLaughlin of Uniquephones.com, in Northern Ireland, has developed unlocking software, but his Belfast-based company hasn't sold or distributed it. He called Apple's warning "something of a scare tactic."

Anyone who has already unlocked their phone could get it back in working condition, he said.

"We have reviewed the source code of a number of these applications, and to the best of our knowledge any changes made to the software can easily be reversed," McLaughlin said in an e-mail. "After unlocking the iPhone, minimal effort is required to get it in to its previously locked state."

As with any Apple product, hacking into the iPhone voids its warranty, Apple said.

Apple has sold more than 1 million iPhones since the product hit the market June 29.