According to BBC and various sources pointed out in Wikipedia The world wide user of IMs are listed below. The Wikipedia IM page User base
AIM: 53 million active users (Nielsen//NetRatings, August 2005), 195 million total (January 2003).
MSN Messenger: 29 million active (Nielsen//NetRatings, August 2005), 155 million total (April 2005).
Yahoo Messenger: 21 million active (September 2005).
ICQ: 15 million active world wide, 400 million total .
Skype: 45 million total (September 2005).
Jabber: 13.5 million enterprise users (Osterman Research August 2005), this does not count users via ISPs and other service providers (estimated to be more than 7.5 million, for a total of at least 21 million).
QQ: 10 million active, 400 million total users (Tencent Q1 results 2005).
Gadu-Gadu: 3.6 million total (January 2005).
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