Apples and oranges.
Exactly. They are completely different devices. The BlackBerry is a robust business tool which is unbeatable for email, messaging and actually phoning people. The iPhone is primarily a consumer device - it's less useful for email and business tasks but the interface is brilliant, the browser is great and the App Store is a significant factor.
If I needed a phone for work, I'd probably get a BB and keep my iPhone for personal use.