I had researched an issue for sometime that we had on a university network regarding wifi calling. T-Mobile does have an excellent document located here: Wi-Fi Calling on a corporate network
But even after implicitly following these detailed instructions, wifi calling was still blocked from working on the system. We employ a Cisco firewall, the key was to enable Cisco ESP VPN protocol on the secure vlans from the firewall. I am posting this to help anyone else who may be managing an enterprise system and is having an issue with wifi calling, as this is what worked for us. Any additional comments or suggestions are welcome, particularly as they relate to wifi calling over an enterprise system.