The Public Switched Telephone Network (PSTN) calling capability in Microsoft Teams is enabled by a specific add-on license, such as Teams Phone Standard or a calling plan. In this scenario, the Teams Phone license was assigned via a Microsoft Entra security group. When Amira was removed from the "Call Center" group, the group-based licensing feature automatically revoked that specific add-on license. Her base Microsoft 365 E3 license does not include PSTN calling, so she lost the functionality immediately upon removal of the required add-on license.

B. A tenant-level setting enables the service for the organization, but individual user access is controlled by license assignment.

C. A network security rule would affect connectivity for a group of users or devices, not revoke a specific feature for one user based on group membership.

D. Browser configuration is a client-side setting and has no impact on server-side license provisioning or feature entitlement.

1. Microsoft Learn. (2024). Microsoft Teams add-on licensing. This document lists the specific add-on licenses, like "Microsoft Teams Phone Standard," that are required to enable PSTN calling capabilities.

2. Microsoft Entra Documentation. (2024). What is group-based licensing in Microsoft Entra ID?. Section: "How it works". This document explains that when a user is removed from a group, the licenses assigned via that group are removed.

3. Microsoft Learn. (2024). Set up Teams Phone. Step 2: "Assign Teams Phone licenses". This guide explicitly states that users must be assigned a Teams Phone license before they can be enabled for PSTN calling.