Long time bb user here too. Have Verizon curve on BES issued by government for work, and had curve 8900 on AT&T BIS for personal. I'll admit the BB push is more reliable, but if I check email on my iPhone it instantly pulls in any that didn't come through push. I can understand wanting instant notice if it's business critical, but don't you have other things you're doing throughout the day for your business? Do you really drop what you're doing and check new emails? Seems not that hard to launch email periodically and get the messages then if they were not pushed.
As for battery I'm finding the iPhone 4 is as good or better than my curve 8900, which was awesome. And the browsing, maps, ability to read attachments are better on the iPhone. That has to be good for business too. Agree with the others. Go to an Apple store and check it out. Good luck