No calls for now. In theory it is possible to make some webrtc calling, but it will go outside blockchain, coz 5 seconds can be count to long for one handshake moment. Also to make it secure (make IPs untrackable) it will make a pretty excess load on nodes.  But everything is possible. Current use cases don't cover calling. But imo it will be great if calls would modify voice (Unfortunately generally voice distortions can be modified back).  I would like Vader voice, or something that is goes from voice to voice in process