[mike-cardwell]

"It would be a funny thing if you needed a key-signing party before you could start to call people on the phone but it may come to that yet."

Voice conversations are actually much easier to secure than other types of traffic. If the two parties know each others voices, then the security of the connection can be authenticated by each party reading back the shared secret, to each other after the call has been established. This is how ZRTP works and Moxie Marlinspikes "Red Phone".