you can not compare BB to iphone if you use it for work.
I received 300+ emails daily x 30 days but it uses only 7 MB for data.
and BB always got mail before my PC. Fast push mail is the selling point for BB.
Never try to teach a pig to sing; It wastes your time and annoys the pig." - Heinlein
Apple has been working to get exchange into the iPhone, but I don't think it would successfully enter the business market as it is still too relying on iTunes. I think it will take at least another year or 1 product generation in order for Apple to enter the business market.
Android on the other hand, is already good at what they are doing. Push Email works brilliantly with exchange and securities are getting there.
I think it is still true that iPhone and other smartphones, are still bandwidth heavy to the current infrastructures we have. BB survives because it is very light in consumption and very flexible.