Here is an interesting list of BlackBerry Storm features that the iPhone 3G lacks. These could make you want to buy a BlackBerry Storm over an iPhone 3G.
Touch Screen Provides Tactile/Haptic Feedback
iPhone owners have long been complaining about the lack of the tactile or haptic feedback. Meaning the iPhone touch screen is not able to provide response when you hit a key which makes it difficult to type without staring directly at it.

The BlackBerry® Storm™ 9530 smartphone has the power and performance to drive your desires. Find out how you can connect to your world.
Easy Touch Screen Navigation
The BlackBerry Storm 9530 smartphone features a SurePress™ touch screen—an innovative, pressable touch screen that allows fast-navigating and accurate typing.
With a SurePress touch screen, typing is easy—simply touch the screen to highlight a letter and then press down to make that letter appear in your message or document. A subtle click lets you know the letter has been entered.