Note: that many of the numbers listed in this section are not directly comparable, and some are speculative. Some instant messaging systems are distributed among many different instances and thus difficult to measure in total (e.g. XMPP). While some numbers are given by the owners of a complete instant messaging system, others are provided by commercial vendors of a part of a distributed system. Some companies may be motivated to inflate their numbers in order to increase advertisement earnings or to attract partners, clients, or customers. Importantly, some numbers are reported as the number of "active" users (without a shared standard of that activity), others indicate total user accounts, while others indicate only the users logged in during an instance of peak usage.
This number is based on the number of Facebook accounts, Google talk and WLM accounts. Further, as there are many other open source servers (some also with companies behind it), the number provided is probably too small. However, many of these servers are not federated, and so, do not actually interact as is usually expected of XMPP servers.
34 million peak online (February 2012), 560 million total (April 2010)
On October 24, 2012 Skype 6.0 connected users on Yahoo, WLM, Skype, and Facebook networks. Facebook excluded, this amounts to 83% of worldwide IM desktop client market share based on data from June 2011.