How to Disable Notifications
When you receive an incoming call or message, you'll see an alert and hear a notification sound or ringtone. The call waiting sound plays when a call is put on hold. You can disable each of these individually.
To access the Settings tab, tap the Settings icon at the bottom of the sidebar. Select "Preferences", then click the arrow button next to 'Alerts and Sounds'.
To turn off all alerts, uncheck each checkbox in the 'Alerts' section.
To silence all ringing and messaging sounds, uncheck each checkbox in the 'Sounds' section.