Auto attendants can be used to create a menu system for your organisation that lets external and internal callers move through the system.

Calls can be automatically put on hold. It includes the ability to search for the next available agent to handle the call, while callers listen to music on hold.

When you get a phone system license for a user, they are able to receive voicemail left by callers. 

These features allow users to make and receive calls directly from the Microsoft Teams platform, be it on their mobile or desktop app.