Google Talk is not available in Iphone App Store, you must add it manually in able to use it in your Iphone. Please follow the this steps:
- In your Iphone, go to your Safari browser.
- Go to this URL talkgadget.google.com.
- Add Google Talk to your home screen by clicking the center button below your browser and selecting add to home screen.
- After that they will ask you for the name which you want to call your site. You can rename it if you like and after that proceed.
- You can now access your Google Talk on your home screen.
Tips: With your Google Talk in your home screen, you can now directly access the website without opening your safari browser. Now it acts as a native App in your Iphone.
See below for the screen captures.