Overview
The Cisco Unified Communications 500 Series can be used for multisite deployments where call processing is distributed. A maximum of 5 sites are supported in such deployments.
Configuration
Multisite_Voice_data_AAG.pdf
Two diagrams are given in this PDF file as an "at a glance" look at the Multisite voice and data CLI configuration required to interconnect 2 sites. It can be extrapolated to multiple sites.
SBCS Multisite deployment Application Note
This goes over the various considerations when deploying multi site and a sample config for interconnecting 3 UC520s using CLI