mobile

First I do not have an S6 yet but am researching before Purchase and main concern
is Battery Life ....but this is a General Question.

On Metro PCS/ Tmobile we already have VoLTE on all Devices which have 4G LTE
Radios which are Carrier Branded Devices.

Metro PCS was one of the first so back in 2012 my little LG Motion 4G had simultaneous
Voice and Data on LTE Band .
My current Factory Unlocked Alpha 850M is CAPABLE of VoLTE but lacks the specific
TMobile Software for VoLTE on this Network so as soon I make a call the LTE
drops down to 3G or H H+ to make the call then returns to LTE after the call.
All unlocked Devices do this .

HOWEVER: the Galaxy S6 has a VoLTE setting in the Menu - on a MetroPCS/Tmobile
version on Tmobile/Metro you already have this function so:
1) What does VoLTE switch do on S6 Tmobile version - you stay on LTE During calls
either way - right ? VoLTE ON or OFF.

2) Since there IS a VoLTE switch will this be the FIRST Device that enables VoLTE even
as a Factory Unlocked version running on Tmobile/ Metro ?

Meaning - is this the beginning of VoLTE as a Universal Android Feature across many
Carriers not requiring specific Carrier Software for a Specific Network to enable
VoLTE on multiple Carriers ?

Thanks for your patience - I am not a Dev and have learned much here.