Following up on #arkOS from the other day is the thought that  voice communication can be brought back from the cloud and onto  ones own  devices. To this I think Mumble is a spot on tool. Encrypted by default, open and free, not too hard to set up a server, plenty of clients for many platforms. Tie this in with a notification system  for  voice chat requests ala GHangouts nd you have yourself a nice space for voice. 
Mumble is an open source, low-latency, high quality voice chat software primarily intended for use while gaming. For Users. Low-latency – great for talking and gaming; Stay private and secure. always encrypted communication; Public/private-key authentication by default …
