Most BlackBerry "native" apps I tried were just glorified WAP apps, not real apps that take advantage of device-specific capabilities, as native iPhone apps do. (WAP is the DOS-like mobile "Web" technology that the cellular industry tried to palm off on us in the late 1990s.) BlackBerry apps -- at least so far -- are incapable of doing the cool things that iPhone apps can do, whether acting as a level or a credit card terminal, managing your Amazon.com orders, or translating foreign-language terms (even hearing the pronunciation, which was handy on a recent trip to Portugal). Awkward interfaces make many BlackBerry apps painful to use, and they usually cost two or three times as much as their iPhone equivalents.
The iPhone has a real OS, and its SDK lets you create real applications, with menus, buttons, interactivity, video, forms, and so on. Plus, you can use Web apps, getting the iPhone's UI for HTML-based functions such as fields and pop-up menus; you can even save the Web apps alongside your other apps for quick one-click access. By contrast, the BlackBerry apps often consist of browser forms and buttons (often at tiny, unreadable sizes) that fetch and display data from the Web. RIM might like to think of them as native apps, but they're really just stubs to Web apps.
Most apps available for business are either personal aids such as tip calculators and expense logs; front ends to sales tools; or basic editors. The iPhone has better UIs for the first two types of apps. For editing, the BlackBerry has DataViz's $70 Documents to Go, which is capable and straightforward, letting me do basic text edits in Word, Excel, and PowerPoint documents, and simple formatting such as boldfacing text. You can cut and paste as well. Tracked changes are removed from the document, and though extensive editing is theoretically possible, you're hamstrung by the device's keyboard and trackball.
On the iPhone, I used the $20 Quickoffice for iPhone, a productivity editor that has similar capabilities (including internal cut and paste), plus retains any revisions tracking in the original document. But it can't work with zipped files. Quickoffice is a little easier to use than Documents to Go, but Apple's prohibition against saving files on the iPhone means that Quickoffice can't get to those e-mail attachments. Quickoffice does have a cool tool to transfer files to and from the iPhone over Wi-Fi, but you need your computer up and running to do that -- in which case, why would you edit the documents on the iPhone?
I also tried the devices on Google Docs. It's barely possible to edit a spreadsheet in Google Docs on an iPhone; the most you can do is select and add rows and edit individual cells' contents. You can't edit a text document, and for calendars all you can do is view and delete appointments. The BlackBerry lets you see spreadsheets one column at a time -- which is useless. Bottom line: Google Docs doesn't support mobile.