I understand it, i would like to see the NPC's in the game already but i see that even if they are not out, you work on the game. I think i bought the game half an y- wait! One and an half year ago. I was playing and it was cool, but then it was a bit annyoing to hear gunshots, helicopters and screams when you don't find vehicles, not-zombified-corpses and survivors as NPC's. From that time you released tons of features/updates/items, you even gave the game a more HD-look! I can wait for the NPC's and i hope most of the others also can. (But still i'm a little confused about why it takes so much time.)
Back to topic :
VOIP would be great, when there was a zombie behind your friend then instead of typing "behind you!" which would take about 2 sec you would use the mic to say it in less than a sec. By this i mean it would be much easier to communicate.