Who I have the same questioned this topic

I need to get the WiFi calling firewall ports and destination IP addresses to add to my corporate firewall. We are trying to allow our users to make WiFi calls since the Verizon coverage is not very good in out building.

I already know some of the ports are UDP 500 and UDP 4500. I need to know if there are any more ports and what the destination IPs are or if there are or the FQDN would work as well.

This is an example from ATT https://www.att.com/esupport/article.html#!/wireless/KM1114459?gsi=FUwZG6c