As answered by the people above it's just an alternative to Teamspeak but unfortunately the plugin is no where near as extensive as ACRE or TFAR. It has no knowledge of objects or terrain and only supports directional audio with distance attenuation.
The advantage it has is compatibility with any ArmA 3 server without modification or effort from the admin. It's just a simple way of having reasonably immersive voice chat with a group of friends.