the iphone screen lock is easily bypassed (or was a few months ago - have they updated it?)
a blackberry on a server can require a password that cannot be forced (enter it wrong ten times and the handset is wiped)
everything going to and from it is encrypted and they can do various kinds of encrypted email.
it is possible to have unsecure data, but once it is put on a coroporate server it can all be managed from the server and unsecure traffic, like internet, can be disabled.
if my blackberry was stolen I could have it remotely bricked in under two minutes and permanently disabled in under five.
you may find though, that govt and banker blackberrys are special models that don't have cameras or bluetooth and require special security measure (ie, smartcards that have to be within a certain distance of the device for it to allow a password to be entered)
should add, I have had my blackberry stolen before and have just bricked mine and had to start from naught again (waiting on my IT helpdesk for a password to activate [grrr])
recently my personal phone has kicked off. The amount of personal info on there was plenty for me to be sad about. Not that some random person would care about my contacts' numbers, but there were a lot in there that I don't know how I will recover.