As for getting TMo WiFi Calling working on non-TMo phones, that's probably possible but will require the right package. The M8 for Windows doesn't have it, sadly.
Also, be aware that messing with install/update packages like this *might* prevent your phone from updating in the future. It's my best guess why my ATIV S was never able to install the 8.1 update (and then it died a few months later, but I'm pretty sure that was unrelated).
Still, this is a great avenue for further research.
EDIT 2: Undo edit 1, it was a pointless suggestion.
Also, be aware that messing with install/update packages like this *might* prevent your phone from updating in the future. It's my best guess why my ATIV S was never able to install the 8.1 update (and then it died a few months later, but I'm pretty sure that was unrelated).
Still, this is a great avenue for further research.
EDIT 2: Undo edit 1, it was a pointless suggestion.
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