I have a Mac at home (Windoze at work) and just got a Blackberry. Can't comment on the iPhone since I've never really tried it. Having an awesome data plan is pretty much a prerequisite to unlocking the full potential of either device, IMHO.
There may be issues syncing your BB with a Mac if you use Entourage:
http://www.crackberry.com/mac-users-...ncing-features