It's NOT possible to stop a outside communication, it's kinda bad if you think about it, the game saying "NO" to your stuff and privacy and closing it up just that you use VOICE-Chatting in-game..
It would be nice to have a voice thingy on the game but you will have to wait a long time so that would happen, the game needs alot of work and maybe..JUST maybe that could get implemented, you'll never know.. and every game like DayZ as peaple using outside programs to communicate with each other and they team up with that.. It's not a big deal, it's fun (:
EDIT:. I don't even know if Unity3D can get implemented voice-chatting.. It would be kinda difficult I think.. or not even possible
I would have more fun using voice communication through skype
Skype, Raidcall, TeamSpeak.. all those programs are used to voice communicate while peaple play games, and must of the players prefer using the programs then the voice thingy in-game
I hope you do understand how game breaking it is to find a camp with perfectly active people who are rather silent, you could also be minding your own bussiness while a group of people is approaching you, and of course you couldn't hear them becuase they are using an outside communication, it really is a serious difference in the game, as for teaming up and long range communication, a radio with adjusted signal could be implemented, something that you could craft or aquire.
My software developing skills are close to non existent, buy I'm still pretty sure that it is possible to implement some protection that would ban such clients, and it's not sad at all, it's like saying implementing a defence from hacking tools is violating my privacy of editing my data.
Hacking and outside communication both give unfair advantage, both use outside programs and both are easy to aquire, I can't see the difference realy, well I can, but you get the point hopefully.
And of course I don't expect it any time near now, just a suggestion.