Here are two great webcasts on integrating LCS 2005 and Exchange 2007 with your existing telephony infrastructure...
Enhancing Messaging with Real-Time Communications
Messaging and calendaring are important, but sometimes what you need is instantaneous, real-time communications. This session describes how to extend your communications environment with Live Communications Server 2005 and Office Communicator to take advantage of enhanced presence, call control, and Voice over IP capabilities alongside your messaging system.
Delivering Anywhere Access: Exchange Server 2007 Unified Messaging
Exchange 2007's Unified Messaging server role allows you to unify voice, fax, and message data into a single inbox that users can access via the web, through Outlook 2007, or on Windows Mobile or Macintosh clients. This session describes the Unified Messaging server role, introduces the new Outlook Voice Access component, and explains how to integrate it into your existing telephony infrastructure.