You would need an Exchange Server for email and a BES for the BB.
You can go to a hosted BES such as mailstreet or exchangemymail for an additional charge over and above the BES rate.
Why not use BIS? I run my own business (Sales, Trainign and Public Sector Business Development) and use BIS for about 8 different accounts, mine and client accounts. Never saw the need for instant email. A lot cheaper too!