AT&T has acknowledged that some iPhone 18 Pro Max devices on its network are experiencing cellular problems, including failures involving calls, text messages and mobile data. The carrier is telling affected customers to install iOS 27.0.1 immediately, even as users report that the update does not consistently resolve the issue.

In a message sent to customers, AT&T warned that some phones may be unable to complete calls, texts or data connections, including calls to 911. The carrier directed users to Settings > General > Software Update and advised them to contact AT&T or Apple with questions.

What AT&T’s warning says

AT&T’s notification describes the software update as an urgent action for iPhone 18 Pro Max owners. Devices affected by the problem can reportedly lose access to the carrier’s network either intermittently or continuously, often displaying SOS mode instead.

Reports from users across Apple’s Support Community, Reddit and other discussion forums indicate that at least thousands of people may be experiencing the problem. The reports describe an inability to place calls, send messages or use cellular data while connected to AT&T.

However, customers have also said that installing iOS 27.0.1 did not restore reliable service on their devices. That suggests the update may not address every cause of the problem, or that additional troubleshooting could be required.

iOS 27.0.1 does not list an AT&T fix

Apple’s release notes for iOS 27.0.1 do not identify a fix for AT&T connectivity problems. Instead, the update is described as addressing a Face ID issue affecting iPhone 18 Pro models.

Apple has not publicly confirmed the cause of the cellular failures. It is therefore unclear whether the problem comes from software, the carrier network or the device hardware. If Apple identifies a software defect, a future release such as iOS 27.0.2 could be needed. A hardware-related cause would likely require a more involved solution.

Why the iPhone 18 Pro Max modem matters

The U.S. version of the iPhone 18 Pro Max is the only new iPhone introduced last month that uses a Qualcomm cellular modem. The smaller iPhone 18 Pro and the iPhone Duo use Apple’s C2 modem worldwide. The iPhone 18 Pro Max also uses the C2 modem in markets outside the United States.

There is no confirmation that the modem difference is responsible for the AT&T failures. Still, the hardware distinction makes it a potential factor as Apple and AT&T investigate the reports.

Owners who receive AT&T’s warning should install iOS 27.0.1 as instructed, but should not assume that the update will necessarily restore service. Customers who remain in SOS mode or cannot reliably make calls should contact AT&T or Apple for further assistance.