Use the dial pad
To dial a number from Teams, go to Calls , and then enter the number of the person you want to reach by using the dial pad. Then select Call. This works for both on-campus Teams users, as well as off-campus, external numbers.
You can also type in the name of a person or group and call them from the dial pad.
Turn a chat into a call
With one click, you can turn any chat into a call in Teams.
When you're in a chat, select Video call or Audio call in the upper-right corner of Teams. The person or group you're chatting with will receive a call from you.
Make a call from your call history, speed dial, voicemail, or contacts
Make a call from your call history:
Go to Calls on the left sidebar and review the History section in the center of the screen. Select any item from the list and then choose Call in the Details section on the right side of Teams.
Make a call from your speed dial:
To access your speed dial, go to Calls and then find the Speed dial section on the right side of Teams. Add people to Speed dial by selecting Add and then searching for their name or number. To add more people, click the "plus" icon on the top right.
Make a call from your voicemail:
To access your voicemail, go to History and select Voicemail in the upper-right corner. To call someone back from your voicemail, select More actions next to their name > Call back from the call history list. Alternately, select Call under the contact details.
Hover over someone's profile picture
Throughout the Teams app, you'll find profile pictures of people you're connected with. Sometimes people choose avatars, or you might see their initials.
Hover over a profile picture and see options to make a video or audio call to that person. Choose one of those options and your call will begin.
Use commands
Quickly find and call people or groups with commands.
At the top of Teams, type /call in the search box, hit Enter, and then enter a name or number. The call will begin automatically when you make your selection.
Receiving a Call
When someone calls you from Teams, you'll get a notification that lets you accept or decline the call, either by video or audio only.
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Select Accept with audio to answer with audio only.
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Select Accept with video to accept the call and enable video as well.
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Select Decline call 
to decline the call and go on with your day.
When someone calls you from outside Teams, the call will show as External and will allow you to Accept with audio or Decline the call.
