Hi,
You can do it but there are some requirements for the WAN link between the servers..
Every 10,000 busy hour call attempts (BHCA) in the cluster requires 900 kbps of bandwidth for Intra-Cluster Communication Signaling (ICCS). This is a minimum bandwidth requirement, and bandwidth is allocated in multiples of 900 kbps.
In addition to the real-time ICCS bandwidth, intra-cluster bandwidth is required for the SQL, CTI Manager, and LDAP traffic. The amount of additional bandwidth is dependant on the use of the system.
Signalling or Control Plane traffic requires additional bandwidth as well.
A maximum Round Trip Time (RTT) of 40 ms is allowed between any two servers in the Cisco CallManager cluster. This time equates to a 20 ms maximum one-way delay, or a transmission distance of approximately 3000 km under ideal conditions.
The only advantage i can see in doing so is redundancy . SRST can't support all the features so in the case of IP WAN failure you will loose some of them. You might have a big remote site and callmanager on site would do local call processing and music on hold as well
You might like to read IPT design guide for more information ...
http://www.cisco.com/en/US/netsol/ns110/ns163/ns165/ns268/networking_solutions_design_guidances_list.html
Marina
