Microsoft Invades iOS, Launches Office Mobile For Apple's iPhone
The catch is that users must be Office 365 subscribers, so it’s not as though this is a suite of standalone Office apps that are optimized for mobile devices; rather, it’s an extension of one’s cloud-based Office 365 subscription.
That said, free app does allow you to open, view, and edit Office documents that have been stored in SkyDrive or SkyDrive Pro and preserves what you normally see on the desktop version (in terms of charts, graphics, and the like), and it has a “resume reading” feature so you can pick up on your phone where you left off on your computer.

Microsoft has completely rethought its iconic Office products by moving to a subscription model and tightly integrating cloud capabilities. The goal with Office 365 seems to be ubiquity and complete accessibility on any and all devices, any time. Thus, in order to fulfill its manifest destiny, Microsoft needs to be available on every mobile platform, and that includes iOS and Android. Phase 1 complete.