The Yahoo! app for the iPhone is in the News category in iTunes, which is a bit odd, since the app does so many things. Most recently the company added voice search to its app, so that you can speak your queries. (Voice search has been available in Google Mobile App for some time.) In addition to offering search, Yahoo's app offers news, e-mail (Yahoo, Google, Hotmail, or AOL), status updates from Facebook, Twitter, and other social networks, RSS feeds, Yahoo Calendar, Address Book, and Messenger — and much more.
It's quite impressive. You can read a short review on MobileCrunch that compares the two apps.