Ok, former hardcore Blackberry diehard here. I said I would never switch to the iphone, but the new 3GS sold me. Nevertheless, I now have some perspective after using both phones extensively :
From what I can tell, the iPhone poses few drawbacks for those who might consider switching from a Blackberry ("BB"). First, Apple could improve the iPhone's battery life. I charge my phone at least once during the day to keep alive during the day but I use it ALOT. I could probably squeeze more juice from a single charge by configuring the phone to auto-adjust screen brightness, to download email less frequently, & to keep me from downloading free apps from Apple Appsstore.
Second, the iPhone lacks the suite of BB email functions every Blackberry user comes to love, but the iPhone is no slouch. A few tweaks by Apple would make the iPhone a formidable contender in an area historically dominated by the BB. One example, having a single inbox that gives you the ability to review all your email from all accounts. Currently, you must review emails on an account by account basis.
Third, & this is a stretch, PIN messages are like instant text messages but they are free. I miss receiving these messages from friends who actively use this proprietary technology found only on BBs. Still, I racked my brain to come up with this last point.
One thing I would probably add to this review which I started writing a few weeks ago is ONE MAJOR DISADVANTAGE of the iPhone if you plan on using ActiveSync. When you reply to a message on your iPhone, Outlook only shows that the message has been read and the Outlook sent folder contains a copy of the sent message. This is really not suitable for someone like me who relies on their phone to send/reply to emails. It is difficult to remember whether I have sent emails or just read them by the end of the day so its a major inconvenience.
I have become addicted to the iPhone in many ways that I couldn't with the Curve, but this single ActiveSync issue could be a motivating reason to reconnect my Blackberry on a data plan (for emails) and use the iPhone for calls, Internet browsing, etc.
If anyone knows whether a solution has been found, then that would be incredibly helpful. Otherwise, switch phones are your own peril. The iPhone is a great device but it hasn't been able to match the Blackberry in the email area.