The state of this active call. The value 'null' indicates that this active call does not actually exist, in other
words it is in the process of being created or destroyed. The value 'off' means that the active call is just being
activated. The value 'try' means that the active call is attempting to establish. The value 'on' means that the
active call is established. The value 'wait' means that the active call is waiting to retry. The value 'await1'
means that the active call is waiting for authentication to succeed before becoming established.