good morning ccweblink.
In terms of the licensing, each user in Teams needs a license:
Learn how Microsoft Direct Routing lets you connect a supported customer-provided Session Border Controller (SBC) to Microsoft Teams Phone.
docs.microsoft.com
I had/have E3 licenses, and had to add extra on the package to get it working.
to get it working:
For the Teams Setup:
https://skalatan.de/en/blog/kamailio-sbc-teams is a very good place to start, for those interested
or for OpenSIPS -
https://blog.opensips.org/2019/09/16/opensips-as-ms-teams-sbc/
is your starting point.
https://www.ferrari-electronic.com/downloads/files/501013/1/EN_QS_SBC-Teams-5-0.pdf <-looks like a good reference.
Fusion does not directly connect to MS Teams, you will have to setup OpenSIPs or Kamaillio, basically a trunk to MS and a trunk to Fusion.