Oh dear dear oh dear..
"existing BlackBerry BES devices which _nobody_ (not even RIM) can snoop on"
Hahahaha, you really believe everything they tell you, don't you? That myth was popped when Middle East countries and India stopped them unless they handed over the keys (Middle East because they didn't want the US intercepting traffic, India because it needed internal intercept).
RIM desperately need this myth, because anyone bothering to check BB settings will discover that all roads (and data) lead to RIM services. Can't imagine a better way to set up global intercept - that's also why BBM use is so wonderful. SMS traffic tends to stay local to a nation (thus requires collaboration), whereas BBM nicely exports it. A similar argument goes for WhatsApp and iMessage, although these two at least don't try to pretend they are secure.
Now, what would possibly convince me to use a wholly proprietary service where I can use one that is proprietary, but has at least some cross platform support (ActiveSync)? Nope. Not a chance. Nice try, though.
Keep on dreaming..