HI,
In the greater story of iChat and Messages iChat started as an AIM client (An app the could join the AIM service).
Apple made an Agreement with AOL/AIM that the then .mac service names ending in @mac.com would be valid Screen Names with the service.
iChat 2 introduces A/V chats in about 2004 in Panther. (OS x 10.3)
(There was a beta for a short time in Jaguar before the Panther release.)
OS X 10.4 saw iChat 3 released which brought Jabber abilities to the app.
GoogleTalk IDs needed a bit of extra work as Google don't follow the general Server Naming trend that every other Jabber server uses.
It also brought 4 way Video chats and 10 way Audio Only chats
http://www.ralphjohns.co.uk/versions/ichat3/ichat3.html
OS X 10.5 brings iChat 4
This adds iChat Theatre (Showing files on your computer as the Video feed including pics from iPhoto as Slide shows.)
Probably most dramatic were Effects and Backdrops plus Screen Sharing
http://www.ralphjohns.co.uk/versions/ichatvers4/ichatvers4.html
OS X 10.6 is for iChat 5 but adds little to what is already there.
OS X 10.7 and iChat 6 add s the Yahoo ability (text chat only)
The Messages Beta comes out during this time and allows a new Account called the iMessage account.
This introduces the ability for the app to send iMessages over Apple's own Service to iOS devices (with the "right" version of iOS)
The full version as it tends to be referred to is released with OS X 10.8
The OS X 10.8.2 update adds the Ability to spoof the iPhone Number (Or use it as an Alias if you would rather) instead of the Apple ID when sending iMessages.
With the change to MobileMe and in some cases linking @mac.com name to @me.com accounts came the change to accommodate these names with AIM.
iCloud @Me.com account have followed.
I have yet to test an @icloud.com name.
This can mean you have an Apple ID from ages ago that ends @mac.com
These tend to work "forever" with the AIM service.
You may also be using as an Apple ID still even it it has lapsed fro some of the paid for services like email.
This can mean you have both an iMessages potential name and an AIM valid name.
7:56 PM Monday; October 8, 2012
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images." No, Seriously