Yahoo! has introduced a new voice search feature in an update to their iPhone app. To access voice search, open the app and click on the Y! icon (with the word "More" underneath) in the right lower corner of the screen.
Then click in the Yahoo! oneSearch box. The keyboard will pop up and a large, spacebar-like box with the words "Press + Speak" will be available. Click on it, say your word or phrase, and then tap again. The app will "think" and then pull up results. The initial results will pull up local options (which are hit or miss) but keep scrolling for typical organic results. Keep scrolling even further for universal options like news, photos, and answers. (See below for screenshots)
I must say, I use the Yahoo! app nearly every day to read the news. (Though, I wish there was an "email story" option directly from the app.) That, along with the Yahoo! Inquisitor app are two of the most useful apps I've seen in the productivity, news, and reference categories. I'm very impressed with what Yahoo! is doing in this space.