So T-MO just announced VoLTE will be available in my area. Does the phone have this capability or will it need an update? They've announced an update for the Galaxy S5 but I haven't heard anything regarding the M8.
I'm pretty sure it's capable of it on a hardware level, it's just a matter of tmobile pushing the update software wise. That being said, it doesn't really do much for you right now other than not having you drop to hspa+ during a call as T-Mobile already does stuff to give HD voice when they can