Wi-Fi calling (Calling preference) setting Lumia 950/XL?

I now had two windows 10 mobile phones which really need wifi calling or they are trash.  Any help?

Thank you.

Hello, Johnathan Brown. WiFi calling features and services are available for a certain operator variants only. This is also depends on your network provider. You may contact them about this concern.

I stumbled across a Microsoft Help page that implies I can enable Wi-Fi calling with this setting:

http://windows.microsoft.com/en-us/windows-10/cellular-and-sim-settings-mobile 

All webpages—which are not under *microsoft.com/mobile—*are from Microsoft and about the generic OS with all features enabled. Only support pages under microsoft.com/mobile are from Microsoft Mobile and relate to your specific firmware and its ‘customization’ (read: limitations) of the OS. Or stated differently: That webpage is misleading because it is not relevant in your case. Anyway, the ‘correct’ answer to your question can be found there…

There, I would go for the button ‘Me Too’. Then you are subscribed to updates automatically. When anything changes, you get notified by E-mail. Furthermore, only one thread must be updated.

Which "operator variants" are available for the Lumia 950 XL?

Because you have a Lumia 950 XL Dual SIM, I am not aware of any operator variant except T-Mobile in Poland. All others are generic region variants. Anyway, to give a general picture: The firmware variant is identified through the Product Code which is printed underneath the battery cover (059…). That code identifies the designated region, country, color, and sometimes the operator of your device. Each variant has another subset of features. Therefore (with Microsoft Mobile), your feature set does not depend on which operator your are using in which country – but where you bought your phone.

I read about tools, which are able to change the customization XML files of the firmware variant. However, I never tested and verified whether those work. Anyway, for the latest available firmware variants for your model type, please, see… (I am not aware of one variant, which gives VoLTE and VoWiFi out of the box).

Just out of curiosity which "operator variants" are available for the Lumia 950XL, which, as far as I know, is only available directly from Microsoft as unlocked here in the US.  Yet the device specs on the website still claim Wi-Fi calling as an available feature (though by your statement appears untrue, or at the very least highly misleading)...  And to your point, I have contacted T-Mobile, and have been told as politely as they could muster to pound sand, citing security concerns and high costs for testing/validating the features.  This current feud between your two companies seems to have left a number of dissatisfied underserved customers in the crossfire...