Official T-Mobile version on Lumia 640 is Windows 8.1 -- There is no Windows 10 update available for official T-Mobile Lumia 640.
You must have a BYOD device that was originally on another carrier (MetroPCS?) or manually updated windows10 (how?). Unless the update comes T-Mobile OTA, the WiFi calling feature would not work.
Thank you matesny,
I thought Windows 10 has this feature without a need of operator customization of the OS.
Yes, it is a BYOD (ATT go phone) but it has the TMo flash and was working with Windows 8.1. Got 10 with windows insider program - like it much better than 8.1.
Does anyone know when an update from T-Mobile is coming?
There is a Software Updates page that lists planned updates for Android phones only. Never a word on software updates for Windows Phone.
As far from what I've read is that the wifi calling feature is activating prior to the OS loading fully. There is no official TMo update yet. TMo usually tests the upgrade prior releasing it to it's customers to make sure everything is working correctly.