When you create a callback, it is possible to set it for another user by using the "Set Callback" field. In this dropdown you are able to see all the other consultants you can set call backs for. An Arithon administrator can add or remove people from this list (see this page: Access Lists).
Please note, that when you set a callback for another user, it will appear in their calendar and desktop, it is not possible for you to put it into their Outlook. All callbacks can be put into Outlook by going to the desktop and clicking the Outlook icon of the relevant callback.