A small number of iPhone 18 Pro Max users on AT&T have experienced a cellular service loss issue. This prevents calls, texts, and data usage, affecting thousands of users. Apple has released iOS 27.0.1 and an AT&T carrier settings update to address the problem. All iPhone 18 Pro Max users are strongly encouraged to install the iOS update immediately. The carrier settings update will download automatically for AT&T users within two weeks. However, affected devices cannot have service reactivated through software updates. Instead, these specific iPhones must be replaced entirely. Affected customers should contact Apple Support, AT&T, or visit a retail store. This issue has only been observed on iPhone 18 Pro Max models with AT&T. No other iPhone models or carriers are currently known to be affected. The underlying cause of the problem has not been disclosed by Apple.