Teams calling is a feature that allows you to provide your users with a Direct Inward Dialing number facility or DID. This allows your users to communicate effectively with customers and business partners who are external to your company. This also allows your customers and business partners to reach you directly using Public Telephony whereas you are reachable on Microsoft Teams with an extension number.

Before you can set up users in your organization to make and receive phone calls, you must assign phone numbers to them. To know more about this you can read an article here

we started off with a project to assign Microsoft Teams phone numbers to our users as their Microsoft Teams extension. This allowed our users to be truly mobile. Their extension numbers that they were assigned during Avaya/Cisco days were no more stuck to their desk. We used AudioCodes as our SBC to integrate our Avaya Telephony with Microsoft Teams. For full post,please read