I get asked this one quite a bit by my customers deploying OCS and Exchange UM to their faculty and staff. I found a partner, 4What Interactive, that provides some really nice end user CBT training for OCS R2 and Exchange UM OVA.
Click here to view some of 4What’s CBT Microsoft UC training. They also can develop custom training if required.
It has voice dubbed CBT training and can also be accessed via the Internet:
UM Outlook Voice Access training: