Of the three Office apps, Excel is the best--which isn't to say that it's great, but that it's the least frustrating of the bunch. It should be noted that there isn't a spreadsheet app on the planet I'd like to use on an iPhone. Even Apple's Numbers, while amazingly useful, leaves a lot to be desired on the iPhone's small screen. But that aside, Excel works well on the iPhone.
The app offers just over 100 built-in functions, which is significantly less than what the desktop versions of Office offer, but what is available should be enough to suit most user's needs. Cell and text selection in Excel worked well, however, I wish the app did a better job of detecting the type of data being edited in each cell. A Numbers-like keypad that knows when you're editing text and when you're editing numbers would go a long way toward saving taps when trying to enter data.
PowerPoint offers the least features of all three apps. PowerPoint is essentially a viewing tool with some minor editing capabilities. You can make changes to text, but really nothing else.
I did plug my phone into my television to see how well it worked as a presentation tool and was pleased by how well it worked.
Office for iPhone has many pain points, so I'll just list a few more. When making formatting changes, particularly when making adjustments at the point where your cursor appears in a document, there were occasions when the app lost its ability to provide a visual indication that a change had been made. So, tap the Bold button and it still looks like you didn't tap it. I found that closing the app from the multi-tasking bar and reopening it resolved this issue. Also, there is no option for cutting text you've selected, you can only copy and paste text.
Unlike normal iOS apps, all the apps in the Office Mobile suite require that you save your documents. If you create a new document or make changes to an existing document then close it, you will be prompted to save your changes. Likewise, if the app crashes while you're in the midst of editing your document, any of your changes will be lost.
Finally, if you're still using Microsoft's .xls format for your files, none of those files can be edited or even viewed using Office for iPhone. In fact, if you have .xls files saved in your SkyDrive, Office for iPhone's file browser won't even display those files.
While Office for iPhone may provide a modicum of value for some users, the reality is that most Microsoft Office users will see no benefit from this app. The app's Office 365 requirement, poor user interface, and odd editing tools combine to make Office for iPhone something you should only use if you have to.
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