Welcome to BBF!
Okay now since you've already held the 8310 from AT&T, have you tried holding and/or feeling any of their 88XX devices--like the 8820 perhaps? That's somewhat bigger than the Curve, you might want to try that. All BlackBerrys can do phone, SMS, emails (up to 10 accounts), organizers (calendar, tasks, memopad etc) and other various business applications. And since you have a Mac like I do, you might want to take a look at Missing Sync and that should meet your sync requirements with your iMac. For other Mac-BlackBerry related questions, you can head on over to the Mac Forums Corner right here Mac Users Corner - BlackBerryForums.com : Your Number One BlackBerry Community
Good luck on the purchase!