I have not perused the MIBS in 15.1(1)T of IOS, but I recently attended a Cisco session where this question popped up. Cisco has introduced several extensions to the CISCO-VOICE-DIAL-CONTROL-MIB and CISCO-DSP-MGMT-MIB mibs. These extensions are specific to CUBE and allow for more granular (i.e. accurate) monitoring of traffic volume. It appears that you can now get aggregate, protocol specific, dial-peer specific, and/or interface specific call rates.
Again I have not looked at this myself, but it seems that you may find what you are looking for with IOS 15.1(1)T. Here is a link that may be a good place to start:
http://www.cisco.com/en/US/docs/ios/voice/cube/configuration/guide/vb-gw-roadmap_ps5640_TSD_Products_Configuration_Guide_Chapter.html
HTH.
Regards,
Bill
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