In today's busy and intensely connected times any early warnings or notifications help users keep on top of calls and meetings.

We believe that if the calls icon in Teams will reflect missed calls(by changing the color or the shape) users will find it easier to return the missed calls without having to click on calls and then click again on history.

The same can be done for the Calendar icon where it can change the shape in case you have upcoming meetings or you are late for a meeting(you don't always have Outlook open and may miss notifications)