Apple says a small number of iPhone 18 Pro Max devices on AT&T have developed a cellular problem that can permanently prevent calls, texts, and mobile data from working. The company says affected phones cannot be restored through a software update and must be replaced.

Apple has released iOS 27.0.1 and a separate AT&T carrier settings update intended to reduce the risk of additional devices encountering the failure. It has advised all iPhone 18 Pro Max owners to install the iOS update as soon as possible.

What affected iPhone 18 Pro Max owners should do

To install iOS 27.0.1, open the Settings app, select General, and tap Software Update. Apple says the carrier settings update will be delivered automatically to AT&T customers over the next 14 days.

AT&T users can also check for the carrier update manually by opening Settings, selecting General, and tapping About. The update is separate from iOS 27.0.1, so users should check for both.

These updates are designed to help prevent the issue from affecting more iPhone 18 Pro Max units. They cannot, however, reactivate a device that has already lost service because of the problem.

Replacement is required for devices that lost service

Apple says owners whose iPhone 18 Pro Max has been affected should contact Apple Support or AT&T, or visit an Apple Store or AT&T location. The company has indicated that the affected hardware will need to be replaced rather than repaired through an operating system update.

Apple has not disclosed the cause of the failure. The company also has not announced whether it will create a dedicated service program for the issue. Customers should therefore confirm replacement options with Apple or AT&T before visiting a store.

Issue appears limited to AT&T and one iPhone model

According to Apple, it has seen the problem only on the iPhone 18 Pro Max when used on AT&T. No other iPhone models or wireless carriers are currently known to be affected.

The hardware configuration differs between U.S. and international versions of the phone. U.S. models use Qualcomm’s Snapdragon X85 modem, while models sold in other countries use Apple’s custom C2 modem. Apple has not said whether that difference contributes to the AT&T-specific failure.

For now, updating promptly is the main preventive measure for iPhone 18 Pro Max owners on AT&T. Anyone whose phone has already lost cellular service should seek support rather than waiting for another software update.