Living in the Stoke-On-Trent area my wife and I can suddenly not receive incoming calls at home. It appears to be related to network switching. As I understand it, when a call is received the handset switches from 4g to 3G. If I call my iPhone from my wife’s galaxy s9, I see the 4g change to 3G but then the call fails. The message saying this phone is turned off or unavailable. Sometimes it will continue to give a ringing tone to the caller but no sound or sign of a call is seen at the receiving end. Shortly after the iPhone will switch back to 4g again. This is repeatable behaviour. If I switch off 4g or switch off mobile data altogether I can receive calls without issue. This is hardly satisfactory as I am paying for 4g. If I need to turn it off to use the phone then I am effectively paying for something I can not use. This issue is affecting both devices in exactly the same way.