Google Mobile team has announced the availability of Google Talk for iPhone users, though its a very interesting development, to access Google Talk from your iPhone you will need to point your browser to http://www.google.com/talk and sign in with your Google credentials to begin chatting.
There are few things which are not yet up to the mark and will definitely need further improvements, the fact that you will have to continuously keep the browser window in focus to keep your chat session active is definitely a dampener. This in plain words means that you once you navigate away from the chat session, by opening a new window or application your status will be set as unavailable, the chat session will be reset the next time you visit the Google talk window.
This may definitely look like a problem when you have to switch between applications to gather some information before IMing it back to your friend. That said the integration in itself is a bigger thing and there will be several improvements over time.