Apple has confirmed an iPhone 18 Pro Max cellular fault that is leaving a number of users on the AT&T network unable to connect to mobile service, with affected handsets displaying only an ‘SOS’ icon where signal bars should be. No cellular connection means no calls, no mobile data, and in the worst cases, no way to ring 999’s American equivalent either.
It’s a grim situation for what Apple has been selling as the best iPhone it has ever made. The 18 Pro Max arrived with variable aperture, a 15-minute 50% fast-charge and all the latest Apple Intelligence features running on the new A20 processor. Without a signal, though, it’s a very expensive slab of glass and aluminium.
What Apple Has Said About the iPhone 18 Pro Max Cellular Fault
Apple issued a statement to 9to5Mac confirming the problem and pointing to two updates as the remedy. ‘We have identified an issue affecting a small number of iPhone 18 Pro Max users on the AT&T network that may cause a device to lose service and be unable to make calls,’ the company said. ‘We released iOS 27.0.1 earlier this week and strongly encourage all iPhone 18 Pro Max users to update now, and are also issuing a carrier settings update today. These updates together are meant to help prevent this issue from occurring.’
There is a catch buried in that statement: prevention, not cure. If your 18 Pro Max has already lost cellular service, neither update will bring it back. The only route for those users is a free hardware swap through Apple or AT&T, covered under warranty as a hardware defect.
For users whose handsets are still connecting normally, installing iOS 27.0.1 via Settings, General, Software Update is straightforward. The carrier settings update is meant to install automatically over the next 14 days, but you can prompt it manually by going to Settings, General, About. There is no on-screen confirmation when it installs, but Apple says the process ensures it has done so.
The Update May Not Be Fixing Much
Here is where things get murkier. According to 9to5Mac, the iOS 27.0.1 release notes made no mention of any fixes for cellular connectivity problems affecting AT&T customers. The update was documented as addressing bugs related to Face ID and camera performance on iPhone 18 Pro and Pro Max devices. Cellular connectivity did not feature.
That omission appears to matter in practice. Early reports gathered by 9to5Mac suggest iOS 27.0.1 is not resolving the connectivity problems for affected users. Many of those who updated when the software dropped are still facing the same issues. Whether the carrier settings update closes the gap remains to be seen once it has rolled out more widely, but the early picture is not encouraging.
Why the Pro Max and Not the Standard Pro?
One detail that stands out is that the standard iPhone 18 Pro does not appear to be affected. A possible explanation lies in the modem hardware. The iPhone 18 Pro uses Apple’s proprietary C2 modem, which CNBC reported Apple’s Srouji described as 50% faster than Apple’s previous modem, adding 5G mmWave support in the US while running at 15% lower energy. The 18 Pro Max, by contrast, uses a Qualcomm modem. Whether there is a specific incompatibility between that Qualcomm hardware and AT&T’s network is not confirmed, but it is the most obvious point of divergence between the two models.
The cellular issue is, unfortunately, not the only headache to have emerged since Apple launched the 18 Pro range last month. There have been three other documented problems since launch: handsets randomly rebooting after a failed Face ID attempt, a cracking or popping sound from the speakers, and some units apparently losing their exterior colour. The 18 Pro Max cellular fault is simply the most disruptive of the lot, given it removes the device’s most basic function entirely.
If you are on AT&T and your 18 Pro Max is still connecting normally, install the iOS update now and keep an eye out for the carrier settings prompt. If signal has already gone, head to an Apple or AT&T store: the replacement is free of charge, and at this point it is probably the cleaner option.
