Many users on a PBX have extension only. Seems wasteful to have to assign them a phone number just to use Microsoft Teams. What are the special settings I need to manipulate to allow me to create the users as Ext only.
 thanks
When you are ready to enable users for Direct Routing, follow these steps:
Create a user in Office 365 and assign a phone system license.
Ensure that the user is homed in Skype for Business Online.
Configure the phone number and enable enterprise voice and voicemail.
Assign Teams Only mode to users.