This chapter examined how Office Communications Server 2007 R2 provides the means for communicating with users of instant messaging services that are provided by MSN, AOL, and Yahoo!. This enables authorized Office Communications Server users to add contacts, share presence information, and communicate in real time with IM users in these public networks. Office Communications Server enables administrators to authorize public IM connectivity on a per-user or group basis and change settings for individual and group authorizations as needed. Office Communications Server also helps administrators control SPIM by configuring message filters to restrict access from unverified users.