Currently my Verizon Wi-Fi Calling on iOS 9.3 works fine at home but not at work (which I control so I can modify it). The two networks have different base stations and routers but I haven't yet found anything different enough between them to account for the non-working Wi-Fi Calling on my work network.

In the article https://support.apple.com/en-us/HT203032 at the bottom in the Get Help section it states in point 3:

Connect to a different Wi-Fi network. Not all Wi-Fi networks work with Wi-Fi Calling.

Is there a list of what is required to make a Wi-Fi network support Wi-Fi Calling? I have yet to find anything other than the ports listed on https://support.apple.com/en-gb/HT202944 about what is needed for a Wi-Fi network to support Wi-Fi Calling.

Does anyone have pointers to more documentation or know what needs to be enabled for Wi-Fi Calling to work? Are there any debugging methods I can try out there?

UPDATE: I didn't end up making any changes on the network and now the Wi-Fi Calling is active. I'm just going to go scratch my head for a while and assume it was an upstream issue I hadn't had a chance to diagnose. Thanks all for the replies and information.