RIM has recently released Blackberry Professional Software which is true Small Business version of BES. It allows both Exchange and BES to run in perfect harmony on one machine.
I'm about to give it a try and see how it goes. I believe the downsides are the lack of enterprise im and mds support, but for small companies looking to house BES in office and without paying for an additional server this a great thing.
Also, it appears to be free to migrate from BES to this product if you are using small business licenses. BlackBerry - BlackBerry Professional Software