This story on AppleInsider has some choice quotes:

Using the web is a “chore” on a BlackBerry but intuitive on an iPhone.

Kraft, meanwhile, emphasizes that the iPhone was brought in to support a “culture change” at the company and that many of those using iPhones are happier than they were before they switched. It pushes the company at large to use newer technology and has been cutting costs by letting iPhone owners get their own support rather than depend on the company alone for help. “Overall they provide better support than we can,” one person from the company’s IT management says.

And…

“We find the BlackBerry better for email and calendaring and the iPhone better for everything else,” he notes.