Blackberry's were intended for business use originally , now everyone has them, as others have posted, instant push email is not going to happen, I think if memory serves me right the BB can be set to check for new email every minute or maybe its instant with the iphone I believe the soonest is 15 minutes or less. As far as IMAP your IT support or network people should be able to assist you with the mail settings and ports. As far as business oriented iPhone, depends on you and your company. Also if an Iphone dies or is in need of repair is there an Apple dealer close by to assist you with that and remember to make backups on your iPhone because the Genius bar is NOT going to transfer your stuff from one device to another, at least from first hand experience I have yet to see it done. Remember you have 14 days to return the device, if you miss it and dont like it sell it on eBay or else where. With AT&T you have 30 days , so lets say u miss the 14 day window but at 3 weeks into it say NO this is not for me than call up AT&T and tell them to remove the iPhone from your account and restore the account to what it used to be or if you were with out contract they can put it back to that for you. Since your new to this I would setup with a temp / new number and if it works for you port the number over after your convinced it will work if your with a different carrier.
Best of luck and I would suggest that you keep an open mind in using the iPhone, if you go the way of jailbreaking your warranty is NULL & VOID
Once again BOL