Microsoft has just released the following Knowledge Base articles (KB972041, KB972042) to address the incorrect calculations of license expiration dates for Office Communications Server (OCS) 2007 R2 and Office Communicator (OC) 2007 R2 Evaluation Edition. The current expiration dates were calculated based on build time, causing the OCS 2007 R2 and OC 2007 R2 Evaluation Edition to expire after June 13, 2009. By applying this fix, the expiration date will be correctly based on installation date of the server.
Microsoft encourages its customers to apply necessary updates in their evaluation environment to take full advantages of the evaluation period.

Office Communications Server 2007 R2
Office Communications 2007 R2
or
Download the latest version of the software trial after June 15, 2009

-Ivan