Network problems after 16.3.1 update…

I would suggest one of the following courses of action:

• Remove your SIM card, check that it is clean and undamaged, and reinstall it.
• Reset your network configuration.
• Contact your service provider and request support.

Best of luck.

UpdateNoGood Said:

"Network problems after 16.3.1 update…: IS ANYONE EXPERIENCING NETWORK PROBLEMS AFTER THE 16.3.1 IPHONE UPDATE? MY IPHONE 12 PRO MAX SHOWS 'SOS' AND NO CALLS CAN COME IN OR GO OUT."

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Troubleshooting SOS:

YouTube this: getting out of sos mode

This is certainly a perplexing issue.

If this is a new device provided as a replacement under a previous warranty, I would suggest making an appointment with your local Apple Store.

If the device was a warranty replacement, it stands to reason that Apple should address faults. As I understand it, if it is a warranty replacement device, the warranty period resets for the new device.

Alternately, it's possible that a member of the store team there can assist further before suggesting that the device be replaced. At the very least they can run a diagnostic on the device to determine if there are hardware faults.

Sorry I can't be of more help.

I had not thought to question if the OP had accidentally enabled SOS mode. Certainly a worthwhile suggestion.