Some iPhone 18 Pro Max users in the United States are reporting cellular connectivity and eSIM problems on AT&T, leaving affected devices unable to reliably make calls, send messages or use mobile data.
Complaints have appeared across Apple’s Support Community, Reddit and online forums since the iPhone 18 Pro Max reached customers, with affected users reporting their devices repeatedly dropping into SOS mode or failing to connect to AT&T’s network.
The issue does not appear to affect every iPhone 18 Pro Max on AT&T, and it is not currently clear how widespread the problem is.
In one Apple Support Community thread, customers describe unsuccessful attempts to resolve the problem through eSIM reprovisioning and AT&T support. One user said the issue persisted after multiple eSIM activations, while Apple subsequently arranged a replacement device after an RF diagnostic test failed to complete.
Other reports describe iPhone 18 Pro Max devices moving between 5G connectivity and SOS mode, with calls, messages and cellular data becoming unavailable even where other AT&T-connected iPhones continue to work normally.
There is currently no confirmed cause.
One notable difference with the iPhone 18 Pro Max sold in the U.S. is its cellular modem. Unlike the smaller iPhone 18 Pro, which uses Apple’s new C2 modem, the U.S. version of the iPhone 18 Pro Max continues to use a Qualcomm modem.
The iPhone 18 Pro Max uses Apple’s C2 modem outside the United States, while iPhone Duo also uses the C2 worldwide. Apple has not explained why the U.S. iPhone 18 Pro Max retains Qualcomm hardware.
There is no evidence at this stage that the Qualcomm modem is responsible for the reported AT&T problems, and the modem difference should not be treated as the cause unless Apple or AT&T confirms a connection.
Some customer reports instead point toward eSIM or carrier provisioning as a possible factor. An AT&T customer writing on Reddit said support described their problem as a known network issue involving phone reprovisioning, although AT&T has not publicly issued a broader statement confirming the cause.
The reports arrive shortly after Apple launched the iPhone 18 Pro and iPhone 18 Pro Max on September 18. The two devices were announced earlier this month alongside iPhone Duo, which opens for pre-orders in October.
Apple is currently testing iOS 27.0.1, an update expected to arrive soon. Apple has already confirmed that an upcoming software update will address a separate Face ID issue affecting some iPhone 18 Pro models.
It is not known whether iOS 27.0.1, a carrier settings update or a change on AT&T’s side will address the cellular problems being reported by iPhone 18 Pro Max owners.
For now, the available reports point to an issue affecting a subset of AT&T customers rather than a general cellular problem with the iPhone 18 Pro Max. Users experiencing persistent SOS mode or failed cellular activation should contact AT&T or Apple for support while the cause remains under investigation.
