Same behaviour here on FP6 with v4.1.1: indeed with airplane mode and wifi on, I could place/receive phone calls. But IMS status of VoWifi remains on “not available”.
Thanks for the feedback that some carriers are now working! That’s great news. However, for my specific carrier, Telstra, VoWifi still isn’t working, and I’ve tried up to e OS 4.2 beta2. Just so everyone knows, the bug is definitely still being worked on. At their request I installed a debug build from the developers which had VoWifi forcibly enabled, but it still didn’t work. Also used the debug build to collect modem logs which contain the agent string that is being sent to the network, the agent string was “Telstra”. Have advised them of this, so hopefully they can make some further progress.