What is Jabber (XMPP)?
Extensible Messaging and Presence Protocol is an open-standard communications protocol. In short, you can use it for instant messaging, file transfer, voice over IP and much more!
Why Jabber/What makes it better than ICQ, MSN, etc.?
Open Source
Jabber is an open system, using open standards. Similar to e-mail, anyone can run a Jabber server and make it available to the public, without having to pay any license fees or sign restricting contracts.
Decentralized Network
Similar to e-mail, there are many providers that offer you Jabber servers. I would suggest Jabber.org (Here is a list of more servers)
Secure
Jabber uses a SSL encrypted connection by default, so sniffing your conversations over the network isn’t as easy as it is with the legacy IM services.
Chat from Wherever You Please
With Jabber you can be connected from several places at once. From work, your home PC, your mobile phone, all at the same time. The places you’re connected from are available as “resources”, and people sending you messages can choose which resource to use, or you assign priorities to your resources yourself.
Create chat rooms
With Jabber, anyone can easily join or create chat rooms where hundreds of people can talk to each other in real-time.
Many clients
There’s not a single Jabber software you’ll need to install to use Jabber. You can choose from a lot of clients which you can also use for your remaining ICQ/MSN contacts who haven’t got jabber yet. (Examples: Pidgin, Miranda, Trillian, Kopete)
Many services
Jabber can automatically inform you about the latest news using RSS, embed your online status on a web page, check your e-mail inbox for new mail, and more.
All settings are kept online on the server, so when you log in to your Jabber account from elsewhere, all your services (and contacts) will be available to you as if you were at home.
Learn More About Your Contacts
Jabber uses vCard to publish personal information. There’s space for your location, e-mail address, phone number, birthday, homepage, hobby list, a photo and lots more. Of course you only reveal what you want to.
Source: http://www.whyjabber.de/index.php?i18n=en
