Teleconferencing is a form of audio voice communication over a network.  The network may be a local area network (LAN), a wide area network (WAN) such as the Internet, the public switched telephone network (PSTN), or any combination thereof.  Typically, a teleconferencing service allocates one or more participant codes to invitees to a teleconference and connects each invitee to the teleconference based on the participant code entered by the invitee after he or she has dialed the call in number of the teleconference service. 
A teleconference usually includes a host, who organizes or leads the conference, and a number of other invitees, also called guests.  The host may often have additional privileges beyond those of the guests, such as, for example, being able to add or remove guests from the conference.  The host may be distinguished from the guests by having a participant code that is different from the participant codes assigned to the guests. 
Instant messaging (IM) is a form of communication over the Internet or other networks.  IM allows for real time communication between two or more users.  This communication is often text based but may include file sharing or other types of communication.  Typically, users log in to IM servers using IM client programs that are located on client computing devices.  These client computing devices range from desktop personal computers to smart phones.  Each user who logs in to an IM server does so using a unique instant messaging ID that has been created to identify that particular user.  IM client programs may be dedicated client instant messaging programs or functions integrated within other programs such as IBM® Lotus Notes®. 
Calendaring functions are typically provided by electronic calendaring and/or email applications.  Calendaring functions allow for the scheduling of teleconferences with one or more invitees and issuing the invitations for such teleconferences to the invitees.  A calendaring function enables the host setting up the teleconference to inform the invitees of the teleconference's topic, date, and time.  Also, the use of the calendaring function enables the invitees to provide an electronic response (RSVP) to the invitations. 
The invitees are typically identified by an email or other electronic address (e.g., internet protocol (IP) address or computer machine (MAC) address) and provide an electronic response from that address.  The invitees typically provide a response (RSVP) message indicating the invitee's intention or ability to attend or not attend the teleconference.  Calendaring functions may prompt an invitee to respond with an acceptance or rejection and then automatically return the response to the host or a meeting facilitator.