Gaping void in default iPhone functionality #123: Real document editing. Solution #123: QuickOffice
You're not going to be able compile any employee-of-the-month-winning spreadsheets on this thing, nor should you try—that's not the point. QuickOffice lets you dive into Word and Excel documents for quick edits, which is all you'd want to do on an iPhone anyway. The price is a little steep, but cheaper than losing your job over an unfortunate misspelling of "public" in the title of a company-wide memo that you just. couldn't. edit.
From The App Developers: Enjoy superior Microsoft® Word AND Excel functionality today in a powerful productivity suite without having to wait. It's all here, right now!