Fairphone Dropped Calls Due to VoLTE and Network Configuration

Verify this by dialing *#*#4636#*#* to access the 'Phone information' menu and checking the 'IMS Status'. If 'IMS Registered' displays 'Not registered', the device is failing to maintain a modern voice-over-LTE connection. Confirm the configuration in Settings > Network and internet > SIMs; if the '4G Calling' or 'VoLTE' toggle is missing or grayed out, the carrier is not providing the necessary network provisioning for the device.