Does the user have a recorded name? The Voice Gateway 2000 gets the name from AD. Did you verify that the recorded name is being attached to the message by the Voice Gateway 2000? You should turn logging for the gateway and post it out here if not. If it is you need to check the configuration on the Meridian Mail.
Also, sending the recorded name is not part of the VPIM specification. This means that the Meridian Mail does not have to support it or support the format that we send it in. For what I recall it did in testing though
Hope that helps,
Keith