If possible, I would like these questions on Instant messaging
answered before 3pm Eastern time on Sun. May 19th.

Interoperability.
1) What other instant messaging systems in AIM interoperable with (AOL
Instant Messager).
2) What IM systems is ICQ internoperable with?
3) What IM systems Yahoo! Messenger interoperable with (I believe it
is interoperable with Microsoft)
4) What IM systems is Microsoft Instant Messenger interoperable with?

Number of users?
1) How many people use ICQ, AIM, Microsoft Messenger and Yahoo
Messenger respectively.

Hi there,

I use all of them regularly, and none are ordinarily interoperable
with any of the others.

However...

Six months ago AOL announced that they would make AIM and ICQ
interoperable (they own both). It hasn't happened yet.

AOL, ICQ to Interoperate -- But in a Limited Fashion
http://www.atnewyork.com/news/article.php/1490771

Trillian
Connects to all four and IRC in a "single, sleek and slim interface."
http://www.ceruleanstudios.com/trillian/index.html

Odigo
Connects with AIM and ICQ
http://www.odigo.org/

Others that attempt to connect them are here:
http://directory.google.com/Top/Computers/Software/Internet/Clients/Chat/Messaging_Services/Unified_Clients_for_Multiple_Messenger_Service/

In my experience they tend to be quite buggy, and constantly need
updating.


Number of users
===============

"According to comScore Media Metrix, AOL (AOL) remains the leader in
instant messaging 34 million people used its service in June through
AOL.com or AOL's proprietary online service while 24 million used a
free, standalone service from AOL. Some individuals used both.

By contrast, 29 million used MSN Messenger from Microsoft and 20
million used Yahoo Messenger. Another 8 million used ICQ, which is
also owned by AOL but not compatible with AOL Instant Messenger. "
(July 2002)
http://www.wired.com/news/business/0,1367,54089,00.html


ICQ
---

"ICQ has amassed over 120 million users in more than 245 countries
since its launch in November 1996."
http://www.icq.com/products/whatisicq.html

"ICQ is a world leading communications community with over 150 million
registered users worldwide."
http://www.icq.com/info/press/press_release46.html

AIM
---

"The AIM community is seen as a particularly lucrative one,
encompassing 30 million active users and 180 million registered
users." (Oct 30, 2002)
http://www.atnewyork.com/news/article.php/1490771

"Enjoy instant access to more than 62 million Internet users
worldwide."
http://www.aol.com.au/site/website/aolproducts/aim/whatis.php

"There have been 100 million registrations of the AOL Instant
Messenger service"
http://www.aol.com.au/site/website/aolproducts/aim/new_features.php

MSN
---

"Now we are excited about bringing this service to MSN Messenger's
base of over 75 million users," (March 12, 2003)
http://www.idg.net/ic_1218780_9691_1-5056.html

"MSN Messenger Service recently reached a record high of 100 million
active users per month worldwide. In addition, MSN Messenger was the
No. 1 instant messaging (IM) service in 11 countries, according to
independent third-party rating organizations during the month of March
2003. (May 12, 2003)
http://www.microsoft.com/presspass/press/2003/may03/05-12100MillionPR.asp

Yahoo Messenger
---------------

"Yahoo!'s network of over 20 million IM users "
http://enterprise.yahoo.com/products/messenger/features/

"more than 20 million users that Yahoo claims use its free Messenger."
http://www.pcworld.com/news/article/0,aid,105681,00.asp


Search Strategy: combining the IM names with "million users"


If any part of my answer is unclear, please ask for a clarification
before rating my anwer.

Best wishes,
robertskelton-ga