iChat is a Mac only app.
An iPhone at version 5 of the iOS has Messages (the current version is iOS 6.0.1)
At Mountain Lion (OS X 10.8 - latest OS X 10.8.2) the Macs get Messages instead of iChat
It adds the ability to iMessage the iOS devices and other Messages users via their Apple ID.
So you have Messages (iOS version)
This can iMessages (Apple's messaging service) to other iPhone Numbers or Apple IDs on iPads, Touches and Macs with Messages.
If you have SMS turned On as well you can SMS non iPhones
If your Buddy does not have Messages on their Mac then you could use AIM Express in a browser if they have an AIM Name)
You could use Google or Facebook in a Browser and user their Chat options if your Buddies use Jabber (Google in GoogleTalk and Facebook both run Jabber servers to be used with their IDs)
There are alternatives like the Skype service that has versions for mobiles and well and PCs and Macs.
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