There is some debate in the industry about bandwidth requirements for Microsoft’s RTAudio and RTVideo codec used in Office Communication Server 2007. This is a very good description of the actually requirements for planning purposes.
The short answer is that you should plan 57 Kbps for Audio and 320 Kbps for Video. The QoE document lists 45 Kbps for RTA-WB, but that does not include Ethernet or SRTP overhead.