When an iphone with wifi calling enabled connects to a wifi system, it sends ISAKMP packets to wo.vzwwo.com. Based on my experience, it appears that If no reply is received, wifi calling on the phone is disabled. I hypothesize this after obtaining packet traces from the phone. I cannot reach any of the IP addresses associated with wo.vzwwo.com -- there are many different addresses associated with this domain name, and the one you get depends on your DNS server. I have spent multiple hours on phone with tier 2 support and had the problem escalated with the result being a reply that summarizes to "you using a Novatel T1114 in a "marginal" coverage area and we don't guarantee connectivity" Bogus. The T1114 has an external antenna, we get 3 bars for data and can xmit/recv as fast as 3-5Mbps. Evidence strongly suggests a routing problem in the network and it is something that occurred about 2-3 weeks ago. I can get no one to look at the issue and actually look at the information I can provide. Since Verizon no longer sells the T1114 nor the data plan I have, it's hard to believe this is not a policy change that occurred with no warnings. I would love to be proven wrong, but the evidence is mounting against Verizon on this.
Further investigation suggests the problem may lie with some wo.vzwwo.com servers. Since my friend in CA was able to traceroute some servers I was unable to reach, I switched to manual DNS on the iphone and the T1114, using Google's 184.108.40.206 and 220.127.116.11 addresses. On reconnecting to the same wifi with phone in airplane mode, I now see 'VZW Wi-Fi' next to airplane symbol and wifi calling is working again. Packet trace shows ISP packets going between the new wo.vzwwo.com and the phone.
How tricky should this have been for Verizon?
Thanks so much for posting this. I upgraded my router and forgot that one of the things I had changed manually was to used Google's DNS. With the ISP default DNS, this feature had stopped working. I went through two rounds of Verizon tier 2 support without a fix.
I have terrible cell coverage at my house but good internet. Wifi calling has been a huge help the past year. I was worried I'd lost it or needed to buy a new phone. I'm so glad I didn't buy a new phone!