iPhone 18 Pro Max update needed
Apple has released a software update to address an issue that may affect phone calls, data, texts, and 911 calls on some Apple iPhone 18 Pro Max phones. If you have an iPhone 18 Pro Max, update your phone to the latest available software (iOS 27.0.1). Go to Settings. Tap General, then Software Update.
Apple also issued a carrier settings update. It will roll out automatically in the coming days. To update your carrier settings immediately, go to Settings and tap General, then About. To confirm you have the latest carrier settings, on the About screen, scroll to the eSIM, primary or secondary section and look for Network AT&T. Carrier should read AT&T 72.1.
Together, these updates are meant to help prevent the issue from occurring.
If your iPhone 18 Pro Max is already without service, contact AT&T or Apple Support, or visit an AT&T or Apple Store. Affected devices can't be reactivated and will require a hardware replacement.