Instant Messaging (IM)

Instant Messaging is an application popular among users of IP networks, such as the Internet, which allows users to have "buddy lists" and send messages instantly between users. Popular commercial products include AOL Instant Messenger and MSN Messenger.

There are two popular standards in the market for instant messaging. One is called SIMPLE, which is based on the SIP protocol, and the other is called XMPP, which was popularized by Jabber.

XMPP was introduced into the market earlier and has a much larger following (as of the time of this writing), allowing people to communicate across corporate boundaries using a number of different client and server software products. Probably most notably, GoogleTalk uses XMPP and can communicate with any company that operates its own XMPP server.

SIMPLE took a number of years to evolve and, as of this writing, was still undergoing development. As such, it was very slow to gain adoption, with product plans of some companies pushed out for more than five years. Worse, it has been said that SIMPLE is far from simple. This suggests that SIMPLE will likely only find utility in environments that must necessarily employ the complex SIP protocol and application servers for VoIP functionality.

Even so, the predominant IM clients in the market utilize proprietary protocols and there are been little motivation to make the products interoperable. In 2006, Microsoft and Yahoo! announced a partnership wherein the two companies would allow its users to communicate with users of the opposite network.

It is important not to confuse instant messaging with real-time text over IP.