For what it's worth, I only observed outbound network activity on port 500 going to IPs with the following pattern:
Perhaps other IPs that don't strictly follow this pattern are used outside North America? Also not clear on when port 4500 is used vs 500 (I've only seen outbound connections on port 500).
It seems that the best way to get an official document from Verizon would be for someone to reach out to their VZW Enterprise account rep. VZW should be happy to share this information, as it would result in better coverage inside buildings and it would prevent Verizon from spending money on repeaters that they often place inside buildings.
vortix we have also only seen outbound connections on port 500 to 141.207.*.232.
I had originally tried reaching out to Verizon around the time I started this thread, but I never got a response. I'm going to try again this week.
I found some stuff here:
I believe as stated above and from testing that UDP/500 and UDP/4500 are what are used for "WiFi Calling". That page has a list of all ports/IPs the wireless extenders use..
I know its late and an old post but maybe this will help someone..