Hi Wissam,

Hope all is well! My understanding of this feature is that it is only supported on Ad hoc conferences (not MeetMe conferences).Have a look;

Conference List:The conference list feature provides a list of participant directory numbers that are in an ad hoc conference. The name of the participant displays if it is configured in Cisco CallManager Administration. Any participant can invoke the conference list feature on the phone by pressing the ConfList softkey and can view the participants. The conference controller can invoke the conference list feature and can view and remove any participant in the conference by using the Remove softkey.

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Note Only the conference initiator can drop any conference party. Any participant in the ad hoc conference can display the list of conference participants if their IP phone has display capabilities. When the ConfList softkey gets pressed, the list of conference participants remains static. The user must press the Update softkey to get the latest list. The list does not update automatically if any participant ends the call or a new participant is added.

From this doc;

http://www.cisco.com/en/US/products/sw/voicesw/ps556/prod_release_note09186a00801e87a5.html#wp1717048

Hope this helps!

Rob