The Unhold command is used to put both legs of the call to InCall state. It only works if a Hold command was initiated to hold both legs of the call.
(Find out what kind of CallStates a call can have.)
It is used the reverse the effect of the Hold command.
Unholds the call the CallChanged notification refers to. Finally the speach engine says to all participants:
"This call has been put back to InCall state."
<Speak Party="all">This call has been put back to InCall state.</Speak>