It is now available on PartnerSource. Unlike SP1, it is not a whole new install, and requires an existing AX4.0SP1 installation. (That is the only upgrade scenario available.)

PartnerSource Link

 Overview

Microsoft Dynamics AX 4.0 Service Pack 2 includes:

~Support for 15 different document AXDs in the Application Integration Framework.
~Updates and bug fixes to functionality shipped in Microsoft Dynamics AX 4.0 Service Pack 1.  Changes include areas such as Financials, BI & Reporting, Client, Cost Accounting, Customer Relationship Management, Developer & Partner Productivity Tools, Enterprise Portal, Inventory Management, Manufacturing, Master Resource Planning, Product Builder, Project Accounting, Application Object Server, and Shop Floor Control.
~Several fixes focused on stabilizing the Client and Application Object Server.  This was a main focus for SP2.

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