If your company is running their BES over MS Exchange, you will notice no difference in speed with the iPhone. I have my iPhone, iPad and MBP connected to a full Exchange server and the iPhone and iPad ding nearly simultaneously where the full Outlook client can lag by as much as 30 seconds to a minute or so - still not a huge issue as I use it only for backing up email, not reading. My corporate phone is a BlackBerry on a BES server over Exchange. I have tested by sending emails to both my personal and work accounts and the iPhone/iPad always get the email before the BB. In fact, when you take the BES out of the equation, even BlackBerries get mail faster...
I dont know if I would ever go back to something other than Exchange for my email. It just works well. All my contacts, calendars, emails are all synched between all my devices (iPhone, iPad, MBP) so effortlessly. I make a change on one, and it is replicated across all other devices nearly instantly. I will always recommend, if someone has access to do it, this method. Not that connecting to gmail via exchange settings doesnt work, it just doesnt work as well. I noticed inconsistencies when I set others up that way.
If you are interested in a full Exchange server for email, there are quite a few out there. Yes, generally there is a monthly charge, but it is worth it. I am grandfathered in to
1&1 Internet - Home Exchange service for $2.99/month because I signed up to beta test it for them about 7 years ago. Been on it ever since and I have never worried about my email. They even give you a full copy of Microsoft Outlook for free when you sign up with them. And no, I do not work for them.
