OK - you are used to installing apps on your iPhones and iPads - first download, and then run the app. You may have to pay for the app - and most of the time, your money gets into the pockets of Apple's App Store even before you actually download the app.
However, things are a little different with the Office Mobile app that lets you run Word, Excel, and PowerPoint on an iPhone - you will soon realize that although the actual app was free to download, you will need to pay for an Office 365 subscription to run the program. To be fair to Microsoft, they have made this obvious on the download screen of the Apple App Store, as shown in Figure 1, below. However, many people do not read all the fine print and even if they do, they expect a free trial, or maybe even a limited, yet free set of features!
Figure 1: Only for Office 365 subscribers!
Note that the very name of the product is Office Mobile for Office 365 subscribers - this clearly indicates that you must have an active Office 365 subscription to use the Office Mobile app.
However, this time Microsoft clearly is in no mood to provide a free lunch for everyone - if you are already an Office 365 subscriber - then yes, this lunch is free for you! On the other hand, many users without Office 365 subscriptions will consider this a very expensive lunch! Major takeaway of this discussion: you will have to get an Office 365 subscription to use Office Mobile on an iOS device.
If you already have an Office 365 subscription, you may get to use Office Mobile on 2, 5, or more iOS devices depending upon which Office 365 subscription you are signed on to. To know how many Office Mobile for iOS licenses are included within your Office 365 subscription, explore our Will my subscription support Office Mobile? page.