iChat is an IM application (Text Chats) that can do Video Chats, Audio Only chats and Screen Sharing.
Face Time is closer to making a Video call instead of a regular Phone call
(if you have it on a Mac, that Mac does not have to be Wifi only the phone has to have a WiFi connection)
iChat also has iChat Theatre (A way of playing/sending as Video) items from other apps.
The iPhoto bit lets you send single pics or Slideshows (with or without the music)
How iChat Theatre looks does depend on the Mac and it's specs that you have.
iChat can use AIM Names.
These include @mac.com and Mobileme names from Apple IDs (not other Apple IDs though)
Since iChat 3 it has been able to use a Jabber Name (These include GoogleMail IDs as they run a Jabber server.
From Lion you can also use a Yahoo name and run a Buddy list that way.
iChat always uses the same Video and Audio Protocols no matter with type of account/Screen name you use.
In the case of Jabber/Google and Yahoo Buddies they have to be using iChat as well.
IF you happen to use a @mac.com name or a MobileMe one then the password needs to be 16 character or less as this is the limit at the AIM servers.
I lied about the link
http://www.ralphjohns.co.uk/ (about 360 pages on iChat 2 through 5)
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb( 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously