A system and method for user-defined control of the operation and appearance of a computerized instant messaging service and associated user interface is disclosed, providing ease of use, control over presentation and access to instant messaging services, particularly for unsighted and other users requiring assistive technologies. A instant messaging (IM) application includes an active sessions list (ASL) comprised of algorithmically ordered identifiers of all communicants in current active chat sessions with the user. The list is presented on the desktop and focused by a predefined first hot-key. By selecting identifiers from the list and activating a predefined second hot-key, chat windows associated with the communicants are opened and focused for receipt of responsive messages from the user.