So out of the box S voice was set to English (US) I couldnt get it to work..I tried "Hi Galaxy" nothing..even made my own "wake up" nothing..Switched it to Spanish and said "Hola Galaxy" and it worked..unfortunately I dont speak Spanish that well so this option didnt work. So my brother told me to switch it to English (UK) and voila it worked 100%..
Maybe its my heavy NY accent i dont know...but i would feel alot better if this wasnt just me..
Mine doesn't work either. If I set language to UK or Spanish it does work. In UK mode when I ask it the weather it shows my temperature as 79C, Ha. Obviously just changing the unit indication without converting.
S Voice US language is working now ... at least for me. It gets network errors from time to time and is as slow as Eskimo snot in winter, but I can now ask my phone what time it is while I try to keep the answer a surprise by ignoring the time at the top of the screen and the watch on my wrist. Fun, fun.