I posted this a while back when another customer was implementing this and I thought it was worth posting again since it’s been updated for February 2012.
This document describes the requirements and processes for provisioning public instant messaging (IM) connectivity for Microsoft® Lync™ Server 2010, Office Communications Server 2007 R2, Office Communications Server 2007, and Live Communications Server 2005 Service Pack 1 (SP1). This includes the following sections:
- Before You Start. Describes the prerequisites you should take before requesting provisioning of public IM connectivity, as well as the information that you need to submit a provisioning request.
- Provisioning Options. Describes available options, including the licensing qualification requirements for each.
- Section 1: Starting the Provisioning Process. Describes the processes for requesting provisioning, as appropriate to each provisioning option.
- Section 2: Important Information about the Provisioning Process. Describes what happens after a request for provisioning is received.
Important: Section 2 includes important considerations for you and users in your organization that can impact the availability and use of current IM accounts. You should review this information in this section prior to requesting provisioning.
WHITEPAPER: Public IM Connectivity Provisioning Guide for Microsoft Lync Server, Office Communications Server, and Live Communications Server
http://www.microsoft.com/download/en/details.aspx?id=14966
Kurt Shintaku's Blog 