It truly is a form v. function issue.
I'll want to use BB messenger, and the email/calendaring/address books ... And I appreciate having a physical keyboard
But the iPhone has a bigger screen, and unless the BB browser is of iPhone quality, that becomes a PITA.
I guess it also depends on what each phone plan looks like as well (as AT&T has jacked up the iPhone base data plan cost by ~$20 /mo)