rs1, Nov 8, 2018 : Current AT&T subscriber. Using a 8/256 6T (got it yesterday). Popped the SIM out of my S7 Edge and put it in my 6T. Used the instructions here (h/t Reddit) and can confirm that VoLTE is working on my 6T! Couple of caveats, my guess is that this only works because my SIM was already active and associated with a device that had VoLTE and VoWIFI. I don't really use WiFi calling, so that doesn't bother (haven't tried to test it either). But the fact that VoLTE on the 6T works with my AT&T SIM is fantastic news! Update: Can further confirm that this isn't just a status icon being toggled. I made a call from my 6T to my work phone and the call stayed on LTE - once I answered the call on my work phone, my 6T showed "HD" on the dialer screen! This rocks!