You won't be able to _wirelessly_ sync with MobileMe like the iPhone. Contacts, Calendar, and (I believe) Notes will sync via USB to/from the desktop using BBDM for Mac. Email can be configured via BIS, but IS NOT the same as on the iPhone (it's not ful IMAP with all folders visible).
You will need:
1. Blackberry data plan. Switch from iPhone data plan. They're not the same. Talk to your carrier.
2. BlackBerry Desktop Manager for Mac. Free from Blackberry. To sync the above items. I would RUN not walk from PocketMac. Too many issues to discuss.
3. Read the BB FAQs as mentioned by aiharkness. Lots of good info on the BB there.
Please research the differences between the iPhone and a BB. They each have their own strengths and weaknesses, and you will probably find one fits your needs better than the other. Obviously, we are all BB fans here
Let us know if you have any other questions, and we'll do the best we can to answer.