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I can also confirm that VoLTE and WiFi calling are working on my Android 9 OnePlus 6T. My phone was purchased via FoneHouse but appears to be non customised as you find buying sim free from OnePlus or Amazon
When I first got the phone with a temporary number I was able to make HD calls (not VoLTE or VoWifi) which uses a 3G signal. However since my number ported I never get the HD call identifier when a call is in progress.
I've not seen any posts on this forum but would be interested to see if others have this working. There is a noticeable improvement in voice quality and clarity for a HD call
I also have a OnePlus 6 running Oxygen 9.0.2
I did the *#800# trick and ticked the two boxes.
After reboot I can now see and enable the VoLTE and Wi-Fi calling option.
I can also see that Wifi Calling is enabled on MyVodafone account settings
But I still cannot make calls when in Airplane mode and Wifi on - also dont see any HD calling logo when not in Airplane mode and connected to 4G network.
So, it seems this works for some and not others.
Come on Vodafone - please add OnePlus to your supported list - Thanks.
I get HD on my OP6 when calling a iPhone on Vodafone. What device are you calling? Does that device get HD icon when calling other Vodafone numbers? (i.e. are you sure the problem is at your end?)
Ok - I rebooted the router and now I see VoLTE in the icon bar - and the HD logo when I call my partner's mobile - yay!
But if I put the phone into airplane mode + Wifi on and try to make a call - it still insists I take phone out of flight mode to place a call. - Ah well one out of two for now...
Well the odd thing here is that your router/wifi have nothing to do with VoLTE or HD Voice, but at least it's working!
I would try someone else's wifi connection, it may be your ISP or router blocking it.
If you dial *#*#4636#*#* (spells info) is 'wifi calling provisioned' enabled under phone information?
I am getting the exact same issue. OnePlus 6, have VoLTE in the top bar. Phone says WIFI calling provision is enabled, but unable to call over wifi with airplane mode on. Same error as you were getting.
Could it just be the Oxygen OS version we are on?
Hi mate, I just rang Vodafone and they enabled it for me.
I was sceptical, but five minutes later and booom..... I have WIFI Calling and VoLTE.
It says VoWIFI at the top. Disable WIFI, and it goes to VoLTE.