I also have the same exact question I've researched the manuals and websites and I've come to the following conclusion:
BES is just a PUSH EMAIL system otherwords fire and forget which really sucks.
I'm heading back to my Treo we also run Sprint Business Connection software which works like BES except I get true sync with email and I can even view our GAL from Exchange. I don't have time to delete 200 messages a day and phone logs when I remove a email from my inbox at the office the phone is automatically syncd up and ready to go. It's really disappointing but I'm looking forward to the Treo 700 once it's out.
Here is the link for the Sprint Biz Connect software:
http://www.sprint.com/business/produ...prise_tabB.jsp
Also why can't you set the message filter to just diplay your email without having to do a
+ i everytime?