Hi Punam,
I don't believe there are any size restrictions;
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.
For each music on hold audio server, you may define up to 50 audio sources. A Cisco CallManager Administration window supports addition, update, and deletion of each audio source. The music on hold server also supports one fixed input source. The system supports the following codecs: G.711 a-law/mu-law, G.729a, and wideband.
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Note: Because the G.729a codec is designed for human speech, using it with music on hold for music may not provide acceptable audio quality.
From this good MOH doc;
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a00803f3a9f.html#wp1027441
Be careful with this issue;
CallManager Failure to Load Large MOH Audio Source Files
From this doc;
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_tech_note09186a00805fef96.shtml
Hope this helps!
Rob
