Tau,
You should be able to use the Product Upgrade Tool (PUT) to see what your available upgrade options are for the customer's contract.
You may want to check out a post from a recent thread by Ron Lifton that explains UCSS:
http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified%20Communications%20and%20Video&topic=Unified%20Communications%20Applications&topicID=.ee835d2&fromOutline=&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.2cc2e7ee
"Hello. Cisco offers a comprehensive and smart way to maximize your investment in Cisco Unified Communications by offering software subscription, service and support. The combination of Cisco Unified Communications Software Subscription (UCSS) and Cisco Unified Communications Operate Service (ESW), allows you to get Cisco's latest software upgrades and updates, including major, minor and maintenance releases, as well as access to online tools and communities that helps you solve issues quickly. Both of these offerings are available for a range of Cisco Unified Communications products including IP Telephony, Conferencing, Messaging, Presence, Mobility and Contact Center.
UCSS is a subscription product that entitles the user to major software version upgrades when linked to an active ESW service contract. Customers are able to stay current by getting the latest product features and capabilities whenever there is a major software release -- at no additional charge--for the duration of the subscription agreement, which can be 1, 2, 3 or 5 years. Many customers will optimize savings and gain the most value for their money with a UCSS term that covers 3 years.
ESW compliments UCSS by providing access to Cisco's latest software application updates, including minor and maintenance releases, and extensive technical support resources.
It's advised to combine UCSS and ESW with UC software so you can increase employee productivity, maintain a competitive advantage and enhance organizational performance by staying current with new software. You can take advantage of UCSS and ESW with either Cisco Unified Workspace Licensing to experience the full power of Unified Communications, or with individual Cisco Unified Communications products."
Brad