Hi Kets,
Here is how to change the MOH for CallManager;
Music On Hold Audio Sources
An MOH audio translator service converts administrator-supplied audio sources to the proper format for the music on hold server to use. The audio translator uses two parameters, an input directory and an output directory. You can configure the input directory, which defaults to C:\Program Files\Cisco\MOH\DropMOHAudioSourceFilesHere, on a per-service basis. The output directory, a clusterwide parameter, contains a Universal Naming Convention (UNC) name to a shared directory on the default MOH TFTP directory. For whatever directory is specified, append \MOH.
When the administrator drops an audio source file into the input directory, the MOH Audio Translator processes the file and then moves it into the output directory along with any files that are generated. Cisco CallManager supports most audio source file formats as input sources, including wav and mp3 files. After the input audio source is converted, an audio source file exists for each codec type that the music on hold server supports. Supply the highest quality source that is available.
From this good MOH doc;
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a00803f3a9f.html#wp1027441
Also,here is a great answer from Jorge that explains things perfectly;
http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified%20Communications%20and%20Video&topic=IP%20Telephony&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1ddbd2c3/0#selected_message
Hope this helps!
Rob
