Is it possible to do a direct upgrade from 4.0.4 to 4.2.1? Do i need a PAK key for it?
This is a supported upgrade path :) Here is the related info;
Release Notes for Cisco Unity Release 4.2(1)
Upgrading Cisco Unity 4.x Software to the Shipping Version
Cisco Unity 4.2 System Requirements
You would need to purchase a 4.x to 5.x Upgrade License if you were going to 5.x or 7.x but not to go to 4.2(1);
Changes to Licensing for Cisco Unity 5.x
Cisco Unity 5.x includes the following licensing changes:
â¢Upgrading to Cisco Unity 5.x requires that you purchase an upgrade license. The upgrade license activates Cisco Unity 4.x licensed features on a Cisco Unity 5.x system.
â¢Beginning with Cisco Unity 5.0, voice recognition is available as a licensed feature.
Obtain the license file(s) for the upgrade to Cisco Unity 5.x.
Obtaining Cisco Unity License Files
License files, which enable the features purchased by the customer, are required for installing Cisco Unity software, for some upgrades, and for adding or changing licensed features. You obtain the license files by completing registration information on Cisco.com.
Hope this helps!