Yammer is Twitter for Corporations. The iPhone application from Yammer allows you to view the latest updates from your corporate network and update your own profile.
You start using Yammer using your corporate email address as your identity. Once confirmed and logged in you can post and view updates, post replies and much more. Yammer also supports groups, which has been added to only partially to parts of Twitter only recently.
This 3rd Party App is available at the Apple iTunes AppStore. Browse the full list of all AppStore apps filed under the AppStore category.