Microsoft 365 Common Area Phone Add-On (Annual Pre-Paid). Maximum 300 Users. This adds Phone System functionality to Microsoft 365 Business Basic, Standard and Premium.
Licensing requirements to integrate Microsoft Teams with phone system functionality
• If using Microsoft 365 Business Essentials, Standard or Premium, either the Common Area Phone License Add-on or the Microsoft 365 Business Voice (without Calling Plan) will be required. The latter includes Phone System and PSTN Conferencing. This is good for up to 300 users.
• If using Microsoft 365 E1 or E3, then the Phone System License Add-on will be required. An optional PSTN Conferencing Add-on is also available.
• If using Microsoft 365 E5, then no additional licensing is needed since this already includes Phone System.