What owners are reporting

• The phone drops from 5G to SOS or no service, even where signal is normally strong.
• Calls fail with "Call Failed" while other phones nearby have full signal.
• The AT&T eSIM fails to activate, or activates and then stops working.
• Some phones worked for a day or two after activation before losing service.

One forum user said turning Airplane Mode on and off brought service back straight away, and Wi-Fi Calling kept working while cellular was down. Others say restarting, resetting network settings and getting a replacement eSIM gave mixed results.

Is it the modem?

Nobody knows yet. The U.S. iPhone 18 Pro Max is the only new iPhone this year with a Qualcomm modem. The iPhone 18 Pro, the iPhone Duo and the Pro Max sold outside the U.S. all use Apple's own C2 modem. MacRumors, which first reported the complaints, says it's unclear whether that's a factor.

Apple is testing iOS 27.0.1, which is expected soon. It isn't confirmed to fix this. Check the release notes when it arrives.

What to try

1. Turn Airplane Mode on, wait ten seconds, and turn it off. Several owners say this brings service back, at least for a while.
2. Turn on Wi-Fi Calling in Settings, under Phone, so you can still make calls at home and work while this is sorted out.
3. Check for a carrier settings update in Settings, under General, then About. If one is waiting, a prompt appears.
4. Install iOS updates as soon as they're released.
5. Ask AT&T to check that your eSIM and account are provisioned correctly.
6. If none of that works, ask Apple to run a diagnostic. One owner says Apple replaced their phone after a radio test failed.

If you're still inside the return window

If your phone keeps losing service and you bought it recently, check the return window with whoever sold it to you, whether that's Apple, AT&T or another store, before it closes. Returning it keeps your options open while Apple and AT&T work out a fix.

If you're thinking of leaving AT&T over this, test another network before you move your number. Most carriers offer a free trial that runs as a second eSIM alongside your current line.