Intercom for Teams: Microsoft 365 (M365) license need

1) Doorbell button calls one Teams user: this user needs a M365 Phone System and a Teams license.

2) Doorbell button call goes to a Call Queue: the Call Queue itself needs a M365 Phone System license (It can be assigned a free M365 Phone system-Virtual User license if there is already one paid M365 Phone system license assigned to one other user within the same M365 Tenant – Details here).
Also, each user that is called from the Call Queue needs a M365 Phone System and a Teams license!

Workaround for 2, if your end-users do not have Phone system licenses:
3) Doorbell button call goes to a Dummy account (this is a M365 account that is only used for distributing the call to a call group). This Dummy account needs a Phone System and a Teams license. On this account, you can configure call forwarding to a call group. All users in this call group will get the call from the doorbell.
The users in the call group only need a Teams license in this case.

Remarks:

The “M365 Phone System and Teams” licenses are both included in an Office 365 E5 license.

In some cases is technically possible, but not advised, to replace the “Phone System and Teams license” requirement by a “Common Area Phone” license (CAP). A CAP licensed user can receive calls but not forward calls.