PGPfone (1995)
en.wikipedia.org
en.wikipedia.org
Really I've never seen any other free software do as good as Jitsi in the VoIP field. I've always tried SIP client and it was never perfect. Jitsi can do SIP to, but does wonder over XMPP so I didn't even try SIP.
Like the other poster said, using various computer inputs to feed the entropy source during key generation is not specific to PGP or public-key cryptography at all.
I'm not sure if it can be used with WebRTC clients, or if it's even needed there.
EDIT: @JshWright - Not sure I understand your question, but RS does "real-time voice communication" (besides the other things like chat, messaging, file sharing, forums, channels...)