Just to be clear about the difference between the Cisco Unified Communication Manager (Call Manager formally) and the Cisco Communciation Unfied Express (CME), the first one is for large enterprises with 30,000 person per Cluster and the CME is for up to 250 users (depending on the router model).
alright now, if you are prepring for CCNA Voice path what you are going to deal with is CME and Cisco Unity Express... and regarding on how to emulate and work with CME, I would suggest the following steps,
1- Download and Install GNS v.3 (Graphical Network Simulator) by following this website http://www.gns3.net/..
2- you can use 3640, 3650, 3735 and 3745 IOS Routers to emulate the Cisco Communication Unfied Express (CME).
by the way, you have to have the IOS images for the routers above to work in GNS and emulate CME.