I took the plunge – I’m currently playing with a BlackBerry 8700g on T-Mobile.
- The keyboard is good.
- Why can’t I be logged into more than one IM network at a time? Odd.
- The interface for this thing is not as friendly as the Palm OS.
- I’m still having trouble believing this… but it appears that it isn’t possible to set more than one “from” address for a mail account. Every mail app I’ve used since Eudora in the mid-90’s has had this, is it really impossible on a BlackBerry? What is the workaround?
- I don’t quite get the IMAP implementation. The BlackBerry received 3 messages, all of which I’ve marked as read on my desktop. When I delete a message on the BlackBerry (even selecting “delete from both server and blackberry”), it doesn’t seem to push that change back to the server. Why isn’t the BlackBerry behaving like a proper IMAP client? This seems like very basic functionality to me…
- How do you file a message in another (IMAP) folder? I seem to be missing something very basic here.
- How do I access my other IMAP folders?
- I can’t get PocketMac to sync my Calendar to the BlackBerry. Support has been fairly responsive, but I’m concerned that the response I’ve gotten so far (some steps to try) is basically all they have to offer and I still don’t have it working.
- I had the “Phone Number: Unknown” problem, the SIM Card menu option is hidden under Advanced Options.
I hope these issues are simply newbie user error – some of them are potential deal breakers for me. 
CrackBerry 
UPDATE: Interesting extreme hack-around for IMAP.