Microsoft has released an Outlook app for iPhone and for iPad, called OWA (Outlook Web App). OWA for iPhone and OWA for iPad are mobile apps that offer the same email, calendar and contact functionality you get in Outlook WebApp on the browser. OWA for iPhone and OWA for iPad can be installed directly from the Apple App Store. A subscription to Office 365 that includes the latest update of Exchange Online is required to use the app.
via Office Blog.