Microsoft Office has finally arrived on iOS in an official app released by Microsoft itself, and it’s free to download, but to use it there’s a considerable catch: you need to be an Office 365 subscriber. Microsoft’s Office 365 costs $99.99 for a one year subscription, and Redmond has really been pushing the SaaS-style version of its desktop productivity suite lately, so the iPhone app is a natural way for it to sweeten the deal for prospective buyers. Microsoft calls the app its “official Office companion optimized for your iPhone,” and the software provides Word, Excel and PowerPoint viewing, editing and creation. Documents are stored in the cloud on SkyDrive, SkyDrive Pro or Sharepoint servers, making them easy to access again from the desktop or other sources, and the app works together with Office 365 to show you your most recently-opened documents on your computer automatically. The app also lets you look at and edit documents attached to emails on your iPhone on the go. Microsoft doesn’t look to have skipped many corners building this app, with support for charts, animations, shapes and SmartArt graphics built-in, as well as a resume feature to pick up editing exactly where you left off on your desktop. There’s offline functionality that commits changes back to the original once you find a connection, and comment sharing and review for collaborative editing. Office for iPhone isn’t optimized for iPad yet, thought it’s hard to imagine that isn’t close behind. And while you require an Office 365 subscription, you don’t actually have to have the desktop version installed anywhere to use this mobile edition, so it is a fairly standalone product. You will need at least an iPhone 4, or a 5th generation iPod touch, running iOS 6.1 or higher, however. And the subscription requirement is sure to be a bummer for many, but the counterpoint of that is that the mobile version is completely free otherwise. Lastly, this is U.S. only for now, but should roll out to other countries over the next little while, according to Microsoft, so if you are geoblocked, just have a little patience.