I can’t make or receive phone calls. Why?

"I can’t make or receive phone calls. Why?: All of the sudden, I can’t make or receive phone calls??"

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Troubleshooting Call Receival:

A. Start Here: If you can't Make or Receive Calls on your iPhone - Apple Support

B. "No Service":

Is "No Service" shown on the top-left corner of your screen? If so, go here to fix that: If you See No Service or Searching On your iPhone or iPad - Apple Support

C. Install a Cellular Update:

It might be prompting you for a cellular update to install. So, go here for that. Update your Carrier Settings Manually on your iPhone or iPad - Apple Support

D. Update the iOS Using a Computer:

• Use my User Tip:  Update your iPhone Using a Computer - User Tip
• IMPORTANT: If you have an option to update, however, then be certain you backup your iPhone first. That way, you will have something to restore your iPhone from should anything go wrong with the update