WordPress posted a note on their blog yesterday stating that they’ve successfully uploaded the application to the iTunes Store, and that it's in a status of "In Review" which means that Apple is conducting their testing procedures. The WP team notes that they haven't been given an ETA but that it could get approved "any time."
WordPress has posted a screencast and eight screen shots of the new application stating "We’ve worked to make WordPress for iPhone a great experience for anyone who’s familiar with the iPhone or using WordPress on the web. With future versions, we’ll continue to incorporate the little touches from the web interface that make WordPress great."
Update: As of this morning the WordPress client for iPhone is available in the App Store and in iTunes.
(Tip: Rob Parker)