Yahoo announced its Yahoo! messenger for iPhone and has also mentioned on their blog that Yahoo! for iPhone is coming soon.
Yahoo messenger blog wrote:
Our new Yahoo! Messenger for iPhone application will be available soon! We announced it tonight in conjunction with the CTIA Wireless conference, so we want to give you a sneak peek at it here on the blog. Check out the demo video below. We’ll let you know when Yahoo! Messenger for the iPhone is available to download!