Apple has officially acknowledged that a select few iPhone 18 Pro Max units, specifically the U.S. variants, are encountering a disruption in cellular service when connected to AT&T's network. These impacted devices showcase an 'SOS' indicator in the status bar and are rendered incapable of initiating calls, transmitting or receiving text messages, or utilizing mobile data. To mitigate the risk of additional devices being affected, Apple has rolled out the iOS 27.0.1 system update along with a carrier settings update. However, for those devices that have already suffered a loss of network connectivity, users are advised to reach out to Apple Support or AT&T for a hardware replacement. This particular issue predominantly plagues the U.S. version of the iPhone 18 Pro Max that employs Qualcomm's cellular modem. Conversely, no analogous problems have surfaced for the identical model equipped with Apple's in-house developed C2 modem in other global regions.