is the echo only during voice calls through the dialogic? if so call dialogic i believe they had a issue with echo on one of the releases of firm ware. if this is on a MOC to MOC call then i would first check to see what the user is using to make the call i.e. laptop speakers and microphone. if they are then try to use a OCS approved USB head set.
and see if that helps.
Mitch Roberson |MCITP:Enterprise Server Admin, Messaging |MCTS:OCS with Voice Achievement |MCT