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You can add a person to an IM/chat in progress if they're also a Business Communicator Collaboration version user. If the person is not in your contact directory, you’ll need to add them to your contacts before you can add them to the conversation.
To add a contact to an active IM/chat:
Note: If you click the handset or phone icon on the communication ribbon in a group conversation, you will call all the contacts in the group. You can call up to 15 contacts from a group chat window.
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