Here's the correct part numbers:
UNITY-LIC-UPG-40 quantity one system to be upgraded
UNITY-VM-USR quantity # of additional users needed
xxx any other features needed
THis is a configured part number so you need both part numbers. If using the configurator tool, start with the part number UNITY-LIC-UPG-40.
Note: if someone needs to add users to a Unity 3.1 system, start with the high-level part number of: UNITY-LIC-UPG-31 quantity one system to be upgraded.