Progress has been made in placing the call, but the contact has not been made aware of the call yet.
This corresponds to SIP's status code 183 Session Progress, and should be used for the period where the CM is waiting for the streaming implementation to initialise (before sending the initial INVITE or equivalent) and when the outgoing call has reached a gateway or ICE negotiation is pending. UIs should not produce a dialtone or start ringing if the call is in this state.