From
http://docwiki.cisco.com/wiki/Unified_Border_Element-_High_Availability_Configuration_Release_9.0(1)
The Unified Border Element box-to-box redundancy High-Availability implementation supports media preservation over an HSRP switchover of SIP to SIP calls. Call signaling preservation is also supported in the latest Cisco IOS Software release 15.2(3)T1.
Another useful config guide:
http://www.cisco.com/c/en/us/support/docs/voice-unified-communications/unified-border-element/112095-cube-hsrp-config-00.html
The RTP streams of established calls are checkpointed between the Active and Standby routers via the HSRP protocol. Therefore the media streams of established calls are preserved over the HSRP failover from the Active to the Standby routers. Calls in a transient state (calls that are not established yet, or are in the process of being modified with a transfer or hold function) at the time of failover are disconnected. Also, any calls using DSP services such as transcoding are not preserved.
There are many others if you google for them.
Chris
