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:
In the chat window, find the contact you want to add to the conversation. (You can use the search feature or scroll through your contacts.)
Click on the contact and drag it to the bottom of the chat window.
If you want to add more contacts, repeat the steps above.
You can also do any of the following from the communication ribbon at the top of the chat window:
To call a contact using your desk phone, click the phone icon.
To call a contact using Business Communicator, click the handset icon.
To video call a contact, click the video icon.
To share your screen, click Start Sharing (the computer screen with an arrow pointing out icon).
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.
To end your chat, click the X on the top right of the chat window.