Note: The following information applies to the IS520.x Smartphone.

The following Video describes, how to enable 4G at the IS520.1 with Android 7. 

This can be necessary for Regions where 3G network is already disabled.

Phone calls via 4G are only possible while VoLTE is enabled. If this is not enabled, the device will try to fall back to 3G and 2G network, so that the quality of the phone call will be limited.

VoLTE: The provider is using the data bandwidth for executing the phone calls. 4G does not have a separate bandwidth for phone calls only as it was with 3G