Apple on Monday warned that unlocking programs used to connect the iPhone to cellular networks other than AT&T's causes "irreparable damage" that would likely result in the modified device becoming inoperable when this week's Apple-supplied software update is released.

Apple also said in a statement that iPhone customers who make unauthorized modifications to the device's software violate the software license agreement and void the iPhone warranty. "The permanent inability to use an iPhone due to installing unlocking software is not covered under the iPhone's warranty," the company said in a statement.

A group of anonymous developers at iPhoneSIMfree started selling this month software that, once installed, would enable the smartphone to work on any service provider with a standard GSM SIM card. T-Mobile is an example of a carrier that would work on the modified iPhone.

Apple said it has found that many unlocking programs available on the Internet "cause irreparable damage to the iPhone's software, which will likely result in the modified iPhone becoming permanently inoperable when a future Apple-supplied iPhone software update is installed."

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

The update planned for this week is expected to add new features, including one that would enable a person to buy music from Apple's iTunes music store over a Wi-Fi connection. The download sets the stage for the iTunes Wi-Fi Music Store. The download site is a partnership between Apple and Starbucks that lets iPhone and iPod touch users download music tracks. The service debuts in New York and Seattle in October.

Apple launched the iPhone in the United States on June 29, making it available only through Apple's retail or online stores, or through AT&T, the exclusive wireless service provider. The company introduced the device in Europe last week; it will begin selling the iPhone there next month. Since its debut, Apple has sold more than 1 million iPhones in the United States and expects to ship at least 10 million over the next year.

This story was modified on Sept. 25 to indicate that the iPhone will be sold in Europe beginning next month.