Solution
Switching between cellular data options in their device settings helped some folks who had the same problem with dropped calls and called failed errors on the same iPhone. If your iPhone is now set to use LTE, for example, you might try switching to alternative options such as Data only. If you want to give it a shot, here's how to do it:
- Go to the Settings tab.
- Cellular should be tapped.
- Select the Enable LTE option. LTE allows you to connect to the Internet quickly, so make sure you choose that option again after you've finished making calls.
- Select other options like Data Only.
After making changes to the settings, reboot your iPhone then try to perform a test call.
