AT&T is warning iPhone 18 Pro Max customers to install iOS 27.0.1 immediately because some phones may be unable to complete calls, send texts, or use cellular data, including when attempting to call 911.
The carrier sent the following message directly to affected customers on Thursday:
Hi, it’s AT&T. Action needed: An important Apple software update for your iPhone 18 Pro Max is available. Some phones may be unable to complete calls/text/data, including to 911. Update to iOS 27.0.1 immediately — Settings > General > Software Update. Please contact AT&T or Apple if you have questions.
The warning marks AT&T’s first public acknowledgment of the cellular problems that have been affecting some iPhone 18 Pro Max units over the past week.
Affected phones can suddenly lose their connection to AT&T, drop all cellular signal bars, and fall into SOS mode either intermittently or for extended periods.
AT&T’s recommended fix is less straightforward than the warning suggests. Some affected iPhone 18 Pro Max units are already running iOS 27.0.1 and continue to experience the same connectivity failures after installing the update.
Apple’s release notes for iOS 27.0.1 don’t mention cellular connectivity or AT&T. The update was released September 28 with fixes that include Face ID problems affecting the iPhone 18 Pro lineup, leaving it unclear whether it contains an undocumented cellular change or AT&T is recommending it as a troubleshooting step while the underlying problem is investigated.
The U.S. iPhone 18 Pro Max has one unusual difference
The U.S. iPhone 18 Pro Max is the only new iPhone in Apple’s current lineup that uses Qualcomm’s X80 cellular modem. The smaller iPhone 18 Pro and iPhone Duo use Apple’s C2 modem, as does the iPhone 18 Pro Max sold outside the United States.
That makes the modem configuration an obvious point of interest as the cellular failures are investigated, but there is currently no evidence establishing Qualcomm’s X80 as the cause.
A network-specific problem, carrier configuration issue, modem firmware bug, or another software or hardware problem could produce similar symptoms.
Neither Apple nor AT&T has publicly identified the underlying cause. AT&T’s message also doesn’t explain why iOS 27.0.1 is being recommended or what customers should do if their iPhone continues losing service after the update.
For affected customers, that leaves an unusually serious problem without a confirmed fix. AT&T is telling them to update immediately because calls to 911 could be affected, while some phones already running the recommended software continue to experience the same loss of cellular service.
