I never did this so I must be missing something, I tried both below but the bridge then fails. Can anyone shed some light on what I am doing wrong. My ITSP now supports in-reply-to so I can pass the caller ID to a forwarded call from FS.

Mario G

  <action application="set" data="sip_rh_In-Reply-To=${caller_id_number}"/>

  <action application="set"><![CDATA[sip_h_In-Reply-To=<sip:${caller_id_number}>]]></action>