You can chat with the contacts in the Corporate Directory. You can chat with contacts in your corporate address book only if they are added as buddies in your instant messaging roster.
To chat with contacts from the Corporate Directory, perform the following steps:
Search the contact from the corporate directory. See How Do I Search for Contacts in the Corporate Directory?
Right-click the contact and select Chat from the drop-down list.
If the contact is offline, the Chat option cannot be selected. If the contact is online, a new chat window opens, and you can send and receive instant messages.