User Interface and Usability
I've been using spreadsheets on mobile devices since the Apple Newton MessagePad first came out in 1993, and for the most part, they've all suffered from the same issue. Spreadsheet apps tend to have a lot of elements that need to be displayed on a screen, so when it comes to common functions, such as formatting cells or inserting formulas, you'll find that the tiny screen seems cramped for space.
Probably the biggest issue I have with Numbers on the iPhone has to do with the fact that it is "stuck" in portrait mode. There's no way to switch to landscape, so when you're working on a cell you generally see about three columns, five rows and then all of the tools associated with whatever it is you're trying to accomplish. You can scroll from side to side and up and down on a worksheet with a swipe, which does make it easier to find what you're looking for, but there's still not a lot of visible spreadsheet.
If you've used Numbers on an iPad, then the UI elements will seem very familiar to you. A workbook can have a number of separate tabs, each of which can contain different elements -- a spreadsheet table, a chart, graphics or even a form for data entry.
Launching Numbers brings up a very simple screen that displays all of your spreadsheets in a grid format. Tap on one to open it, tap the "plus" button to add a new spreadsheet or press edit to perform actions on the sheets, like duplicating or deleting. You can also just tap and hold the spreadsheet icons to go into jiggle mode, and then perform actions on the sheets.
Once a particular Numbers sheet or workbook has been opened, you see a very small facsimile of the sheet on the iPhone screen. The standard reverse-pinch gesture zooms in on the page, and swiping moves the focus of the sheet. To edit an element, you double-tap on it. For example, double-tapping a chart lets you edit the references to the source spreadsheet, while double-tapping a sheet brings up a keyboard. Depending on what you want to put in the cell -- a formula, text, time and date or a number -- the keyboard changes. Of course, some formulas can be quite lengthy, so the formula bar actually scrolls with a simple swipe.
To add elements to a blank sheet, there's a button that looks like a small picture. With a tap, you can add media from your Photo Library (including short movies), tables (which are the empty spreadsheets), charts and shapes. Like the iPad version, there are a number of different color combos and types for each element.
Comparison to Quickoffice Pro
Up until this point, my choice for a mobile spreadsheet has been Quickoffice Pro ($9.99). While I think it is lacking in the sheer number of features that are packed into Numbers, it does have integration with Dropbox, which is something I find very useful. On the other hand, Numbers works with iWork.com and will work with the upcoming iCloud service.
The user interface of Quickoffice Pro is more stark, but very usable. The app includes a tremendous number of built-in documentation and help files, which are useful when first learning how to use Quickoffice Pro. However, Numbers has very well-written and logical help files, which I highly recommend to anyone who wants to learn the app.
The big advantage of Quickoffice Pro is that it uses Microsoft's .xls and .xlsx file formats as its native formats. It also works with Numbers files, and it also does an awesome job with Word and Pages documents and PowerPoint and Keynote presentations. However, I think Numbers does a much better job of mixing in different media types in a single workbook.
While Numbers on an iPhone would work in a pinch, I'm not sure I'll use it on the device unless I absolutely have to. On the iPad, the app works very well; on the iPhone, the lack of screen real estate makes it very difficult to use. I think this is going to be a common theme with the iPhone iWork apps, and I'm curious to see what my fellow bloggers Mike Rose and Megan Lavey-Heaton have to say about Keynote and Pages respectively.
Since Numbers is a universal app, if you already have it installed on your iPad it's a free download for your iPhone or iPod touch. In that case, by all means go for it. But if you're looking for something that might be a bit easier to use -- albeit with far fewer features and finesse -- Quickoffice Pro or any of the other iPhone spreadsheet apps might be a much better choice.
If any TUAW readers have also downloaded and used Numbers on your iPhone or iPod touch, I'd love to read your comments.