Now that I have an iPhone, and since I've had a Blackberry for about 6 years, I know you've been wondering what I think of them in comparison to each other.
I have had a "blueberry", 8700, and I've had a Curve 8300 for over 2 years now.
I have never used the phone function on the Blackberry because I've not wanted two phones. So I've always used my personal cell as my mobile contact for work and personal calls. I added my personal email to my Blackberry a couple years ago, and I have the AIM and Y!Messenger applications on the Blackberry. A couple weeks ago, my company switched over to Microsoft Exchange so I added my work email to my iPhone. I decided to compare the two by leaving one behind for a day and just working off of the other. Here's my conclusion.
The iPhone is more fun. The Google maps is quicker and triangulates better so that it shows me where I actually am. The BB is often off a couple hundred feet. The applications on the iPhone are addictive and I would choose it any day for my personal life.
The Blackberry is a better tool. The email, IM, and SMS are all in the same view so you don't need to switch between applications to stay in touch. There is no delay when accessing your contact list to send a message - in any format (mail, IM, or SMS). These are the two most frustrating things about the iPhone - switching between applications and the way it hangs up because it needs to connect through the Internet to the exchange server for my work contacts. If you exit the IM applications, they are no longer running, and therefore, you are not available unless you are actively in a chat. Yes, the applications I loaded said they "push"; but they push to email... and if you are in mail and get an IM, you have to close mail, navigate to the IM app, and load it. My Blackberry shows me my email, Y! and AIM chats, and Blackberry messenger chats all in the same view.
These limitations make the iPhone frustrating to use as a work tool. Perhaps if I only had the iPhone I wouldn't notice the differences in a way that matters. Since I have the Blackberry, I will have to say, that I would chose to stick with it for work.
Even though I was really hoping to give up one of these devices so that I didn't have to walk around all day with both, I can't do it. I guess I just have to make sure I have a big enough purse and two back pockets.