> Enabling group administration was also a hard feat, as Signal has to give administrators the ability to add and remove members without its servers knowing who's part of the conversation.

I was chatting with Trevor Perrin about abstract crypto relating to this when he was presumably working on this, and never got the chance to ask him - even if the group crypto hides this information, the Signal server still has to physically deliver the messages to the correct people in the group, whose phone numbers are all known by the server, so isn't this exercise a bit pointless? Or are there long-term plans to drop the critical reliance on phone numbers?