Fix no service on iPhone.
if u see no service message on the iPhone screen it's mean your device is in a critical situation and then you won’t be able to make or receive phone calls or connect to the internet unless you are using Wi-Fi, or send messages.
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How do you fix no service on iPhone? | Howtoifixit.com
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How do you fix no service on iPhone? | Howtoifixit.com

To fix no service on iPhone, you have to check if you are in the coverage area, reset network settings or update the software.