I have a BB 8830 through Sprint at work and my wife has an iPhone.
I will echo what others have said on here. For work/business the BB wins hands down. Push e-mail, task management, and full keyboard are far better than on the iPhone.
iPhone is nice for casual business use and the iPod and camera functions are nice, but I would go nuts if I had to use it for business as my only device.
Also... 8830 has GPS navigation built in that works quite nicely. Plus EVDO speed is far better that lame EDGE on iPhone.
Now when they come out with an iPhone with GPS and a true 3G speed network and real task management, you might have something.
Even then, I think a real keyboard will always be better than the iPhone touch keyboard for heavy users.
Hope this helps you decide.