Been having issues with connecting to a T-mobile MVNO's Wi-Fi calling ever since I switched to 5G Home Internet with FastMile 5G Gateway 12.
I use Airplane mode during tests to ensure only the wifi calling and not regular cellular connection is being tested.
Wi-Fi calling often did not connect. Even if it did connect, the calling and texting did not work. Would get call failed when trying to initiate outgoing call, and outgoing texts would error out with message not delivered.
It used to work seamless with my old ISP, and still works flawlessly on other WiFi networks.
After tinkering and eliminating other variables per AI suggestions:
- Home router, worried about possible double NAT - so tried directly Nokia modem/router - no success
- Firewall: disabled, ALG: disabled SIP and IPSEC, MTU size: down from 1500 (auto default) to 1380 and 1420. Nothing worked.
Supposed core network CGNAT or possible blocking or throttling of Wifi calling by Rogers would make wifi calling impossible, was going to give up on 5G internet and switch to regular wired internet.
Tried to use VPN on iPhone to bypass any wifi calling specific filtering or blocking issues - still didn't work. However, apparently, AI suggested VPN on iPhone does NOT proxy some system services like wifi calling (not verified). Could have a tried a whole network VPN or do Internet sharing from a PC running VPN, to tunnel all of the iPhone's traffic, but didn't have to get there.
Ultimate fix: Switch to IPv4 or IPv4&IPv6 from IPv6 only
- Visit Nokia router Web Admin UI 192.168.1.1 or gateway IP
- WAN -> WAN services -> Cellular (tab) -> Pick default APN
- Set IP mode to IPv4 or IPv4&IPv6
Both of those modes seem to have fixed Wi-Fi calling. I'm leaving on IPv4&IPv6 for now, will switch to IPv4 only if I encounter further issues.
Not sure issue is from T-mobile's wifi calling servers, Rogers IPv6 routing, or some adverse reaction.
Hope this helps someone else