Signal - we are using it at the first place for mobile communication.
It is info-safe because of data encryption, so we can send messages, data (images or movies) and also call. There can be made groups or you can talk individually. It uses telephone numbers, not internet.
Just download it from mobile store.
At first run you must set up application. Only insert your username, password and telephone number. After this you can add your teammates to chats.
- Application doesn't notify me if someone calls me by Signal
Go to application settings, then into Notifications and change Repeat alarms (change for 5-10 times), also go into Priority and switch on Ignore not disturb mode.
After this operations you should see notifications at the top of the system bar and also they should appear on unlocked/locked screen.