UNITYV5 = Unity Version 5 Software
Unity 5 allows for dual licensing in UM setup so users can be assigned a Voicemail or Unified Messaging license. The users still have to be setup in the message store (Exchange or Domino), but you don't have to pay for a full UM license for a common area phone that requires Voicemail only. The users that are setup as Voicemail only don't have access to the Text-To-Speech engine for e-mail and fax playback.
The part number UNITYV5-USR-E10= is for 10 Voicemail users on a Unity System that is setup for Unified Messaging using Exchange as the message store.
The part number UNITYU5-USR-E10= is for 10 Unified Messaging users on a Unity System that is setup for Unified Messaging using Exchange as the message store.
The UNITYV5 part numbers also apply to VM only installs. They've tried to make it a little easier when it comes to Unity 5 licensing.
HTH
Thank you,
Jon Nelson