Update at the bottom of the article
After playing around with the LG G3 which is my daily driver on T-Mobile, I found in the hidden menu that the T-Mobile LG G3 indeed supports VoLTE, but its not official yet by T-Mobile. so you will be able to enable/disable it only at the hidden menu, Currently T-Mobile has around 5 phones which supports officially VoLTE and most probably the LG G3 will be the next phone to support it.
To enable/disable VoLTE:
Scroll down to LTE
Now click the VoLTE and in there you will find a option to enable or disable
Take note that the phone needs to perform a restart to take effect.
Most of all as its not official yet and as T-Mobile doesn’t cover yet all areas with VoLTE the phone might actually not work on VoLTE even its enabled.
If you enabled it and you made a call on VoLTE let’s us know in the comments below where you live and how it worked.
Will keep all of you T-Mobile LG G3 customers know once T-Mobile makes it official until than enjoy our workaround and spread the word!
UPDATE: We reached out to T-Mobile regarding VoLTE for the LG G3, T-Mobile was kind enough to confirm with us that the LG G3 will be getting VoLTE very soon with the next update.