First off, with BIS it is only one-way email reconciliation since the system is designed that way. It is also not designed to read the folder structure, etc.
BES does do all of the agove but the BES hosting service probably requires Outlook because they have most likely setup the BES with Exchange. The other possible options would be Domino or GroupWise. They would give you a new email account on the Exchange so forget the IMAP account. This new account would be setup for email, address book, calendar, memo and tasks which would all be wireless.
You would need the Enterprise plan to be on a BES.