The information you are looking for is contained in the Unified Communications Technical Information Sites. The landing page for the sites is located at http://cisco.com/go/unified-techinfo
In the right-hand navigation panel you will find links for the Release Compatibility Matrices for both IPT and Contact Center releases. This show the combinations of Unified Communications product releases which have been tested together for compatibility and released as a system.
Similar information for releases not contained in the matrices is found in the System Compatibility Tool, listed just below the matrices on the landing page.
Hope this answers your question.
Carol Thorsten-Stein
carolts@cisco.com