Smartphones are the multi-tools of electronic gadgetry. I used to use my Palm Treo as a memo pad, storage device for my electronic passwords, shopping list, and of course an Internet access device and PDA. That kind of versatility is the iPhone's big lack. It's great at what it does, but you can't even transfer memos from the iPhone to your desktop.
iPhoneDrive takes a small step toward making the iPhone more of a general-purpose tool. It's $10 Mac software that lets you copy any file and store it on your iPhone as if it were a hard drive or a thumb drive.
The user interface looks like the Mac Finder. You install it the normal way you install Mac apps. You can transfer files to the iPhone either by clicking the "Copy to iPhone" button in iPhoneDrive, or you can drag them from the desktop or browser window into the iPhoneDrive window. Copying from the iPhone is similar: Click the "Copy from iPhone" button in iPhoneDrive, or drag from the iPhoneDrive window to the destination location.
This software isn't a reason to buy an iPhone. You'd have to be crazy to spend $500 on a 4 GB thumb drive; you can pick one up at Amazon.com for $41. But it's a good way to get more out of the iPhone you already have.