SIM locked 0 attempts message keeps popping up intermittently when Existing SIM card is placed in new iPhone12 Pro Max…. No service status lines HOWEVER: work perfectly still and not locked in old iOhone in

Hi there Ziekie,

Thanks for joining us in Apple Support Communities! We understand you're seeing a message that the SIM card in your iPhone is locked. We're glad you're here, and we can provide some guidance.

"To protect your SIM card from others using it for phone calls or cellular data, you can use a SIM PIN. Then, every time you restart your device or remove the SIM card, your SIM card will automatically lock and you'll see "Locked SIM" in the status bar."

Keeping that information in mind, it sounds like you're using a SIM PIN with your iPhone. To find out how to turn the SIM PIN on or off, have a look at this support article:

Use a SIM PIN for your iPhone or iPad

We hope this information is helpful. Don’t hesitate to let us know if you have any more questions.

Cheers.