I can't make voice calls

The selected network mode is not available

Turn on automatic network mode selection.

1 of 8 steps Slide your finger downwards starting from the top of the screen.
2 of 8 steps Press the settings icon.
3 of 8 steps Press Connections.
4 of 8 steps Press Mobile networks.
5 of 8 steps Press Network mode.
6 of 8 steps Press the required network mode.
7 of 8 steps Press the Home key to return to the home screen.