There are two types of on-hold features which can be configured on a Call Manager 3.2 (i am not sure of version 3.3)
1. Music on Hold
2. Tone on Hold
Tone on Hold is enabled by default and cannot be disabled.Where as Music on Hold can be enabled, provided the audio file exists in flash.THe command used for this are:
telephony-service
moh music-on-hold.au
More explaination of this can be found at the following url:
Configuring and Troubleshooting Cisco IOS Telephony Service (ITS)
http://www.cisco.com/en/US/customer/tech/tk652/tk701/technologies_configuration_example09186a00800ffdcc.shtml#otherITS
As far as the Call Manager 3.3 is concerned, I am not very sure of the on-hold features.You can check this out in the url
Cisco CallManager 3.3
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_data_sheet09186a008010a821.html