Unified Communications Options

Teams users can take advantage of the Office 365 Phone System, which is in the Microsoft cloud. This is the same phone system that is used by Skype for Business online. For users, that means they can make and receive calls from the Microsoft Teams client.
The benefit of using the Office 365 Phone System is that it gives the Private Branch Exchange (PBX) capabilities without the complicated and expensive equipment. With the Phone System add-on, Microsoft Direct Routing Teams and Skype for Business Online can be used to complete basic tasks, such as making and receiving calls, transferring calls, and muting or un-muting calls from nearly anywhere with internet access.
The Phone System can be connected to a telephony network in two ways:

• Obtain a Telstra Calling for Office 365 plan. This option means that Microsoft not only provides the Microsoft Phone System, but utilize Telstra as their back end Cloud Carrier
• The second option is to interconnect a carrier/telco to the Microsoft Phone System through Microsoft Teams. In this case, Microsoft will provide the Microsoft Phone System and access to the telephony network will be from a third-party carrier. This is referred to as Direct Routing.