This has been a popular topic on the TechNet forums.The OCS mediation server previously stripped out the caller name from inbound and outbound calls that pass through it. Now with the latest OCS R2 patches, this feature has been implemented and I am here to testify that caller name is now passed inbound and outbound. Even though the Kb article outlining the changes to the mediation server do not mention the feature, the changes are certainly in there. Inbound the caller name appears in the toast that appears on the inbound call but it is not displayed in the call window.
The mediation server requires upgrading with the patches. This will automatically enable inbound caller name. Outbound caller name requires a .conf file. See the KB article here for creating the required file. The file creation and insertion is simple but it is required on every mediation server in your network you require caller name.