Microsoft is releasing another Office app for iOS today, kind of. The new Office Web App for iPhone and iPad is designed for businesses who use Office 365 to access the full functionality of Outlook Web App. Although Microsoft has been supporting a web version of this previously, the software maker has packaged it up into a "native" app for iOS. If your work place subscribes to Office 365 then the benefits are clear, but if it's not then it's useless for those thousands of Exchange servers that run in enterprises today.
The app does package together Mail, Calendar, and people into one neat package though. There's also a navigation screen that includes Live Tiles of information. Microsoft has built in voice input too, allowing users to executive commands like "open Calendar for tomorrow." Most of the UI is very similar to the existing Outlook Web App for Office 365, and apps for Outlook will work here too. The big reason you'd want to use this is for offline email, and the OWA for iOS app allows users to read, delete, flag, reply, and compose new messages while there's no internet connection. There's no additional charge for Office 365 subscribers and the app will be made available in 60 languages.
Update: Microsoft says "support for Exchange on-premises is planned for the future," meaning there won't always be an Office 365 requirement.