Why is my iPhone 6 not making or receiving calls?
Why is my phone not making or receiving calls
[Re-Titled by Moderator]
iPhone 6, iOS 12
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Have you changed carriers?
See this Apple articles below:
If you see 'invalid SIM' or 'no SIM' on your iPhone or iPad
https://support.apple.com/en-us/HT201420
How to unlock your iPhone for use with a different carrier
https://support.apple.com/en-us/HT201328
If you can't activate your iPhone
https://support.apple.com/en-us/HT201407