Apple did not erase iChat.
Messages in Mountain Lion is iChat +
The plus bit is the fact you can iMessage iOS devices.
All the other features that were in iChat are still there.
If you upgraded Lion to get to Mountain Lion then in System Preferences > Mail, Contacts and Calendars you probably list all the iChat Accounts (Screen Names and IDs).
You may need to enable them for Messages.
They should also show up in Messages Menu > Preference > Accounts
Once those accounts (AIM and Jabber) are Enabled they can be viewed in a Combined Buddy List
Windows Menu > Buddies (Or using CMD + 1 Keystrokes)
In the General Section of the Preferences you can Unlink these Buddy lists.
The Green icons or highlight a Buddy and then using the Buddies Menu or the icons at the Bottom of the Buddy list can be used the same way to start Video or Audio Only chats.
The iMessage "Account" is only for texting iOS devices or other people using their Apple ID on a Mac in Messages.
It is an account "in addition to" rather than "taking over from" the services that iChat can join.
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