Some iPhone 18 Pro Max owners in the U.S. can't use AT&T's network for calls, texts or data, with complaints piling up on forums, Reddit and Apple's support community, MacRumors reports. The U.S. Pro Max is the only new iPhone this year with a Qualcomm modem instead of Apple's own C2, which makes it an obvious suspect, though nobody has shown it's the cause.
AppleInsider heard the same thing a day earlier and says AT&T has acknowledged the problem, while Apple has not. The trouble seems tied to eSIM setup. Calls still go through over AT&T Wi-Fi Calling, but on cellular the signal wanders or sits on SOS. Apple is testing iOS 27.0.1 for release next week, which may carry a carrier fix. If you bought at launch, you're still inside the 14-day return window.