There's no iChat app for the iPhone 4s to be able to instant message chat with those you normally speak to on your computer?
Surprised Apple hasn't made an iChat application. It should be built into the phone already but to create an app would be simple. You would then be able to video chat with people on computers as well which would be cool instead of having to go through FaceTime.
There's evidence we may see iMessage capability in iChat: https://www.macrumors.com/2011/09/14/apple-is-building-imessage-into-os-x-lions-ichat/
As to videochat with people on computers, FaceTime exists in OSX, or just use Skype.
What Google Talk app?
FaceTime doesn't exist on mine and they would still have to download the software and install it.
Meebo
I recommend Beejive IM. Well worth it.