InvitedUser -> InitiatingUser: STEP_2_SEND=transmit InvitedUser ContactCard (QR Codes, Bluetooth, messaging, mail, ...) encrypted with initiating user pub key
InitiatingUser -> InitiatingUser : STEP_3=InitiatingUser_Id Accept Invitation and create answer (Generate InitiatingUser ContactCard and create finalized InvitedUser contact)
InitiatingUser -> InvitedUser: STEP_3_SEND=Send answer through invited user's message servers from contact card
InvitedUser -> InvitedUser : Finalize InitiatingUser from its ContactCard
InvitedUser -> InitiatingUser: STEP_4= Send confirmation to InitiatingUser that communication is possible through initiating user's message servers from contact card