Cisco Unified CallManager provides a scalable, distributable and highly available enterprise IP telephony call-processing solution.

Cisco CallManager software extends enterprise telephony features and capabilities to IP phones, media processing devices, voice-over-IP (VoIP) gateways and multimedia applications. Multiple Cisco CallManager servers can be clustered and managed as a single entity—a unique capability in the industry.

Some of the enhancements provided by Cisco Unified CallManager offer the following:
     + video telephony function
     + multiple calls per line
     + call join
     + direct transfer
     + immediate divert
     + ad-hoc conference list
     + drop any member
     + improved security
     + interoperability
     + functionality
     + supportability

CallManager also has many security features that give users the ability to verify identity of the devices or they communicate with, ensure the integrity of data it is receiving and provide privacy of communications via encryption. View PDF.