I'm on SherWeb (http://www.sherweb.com
) and am happy with them. However, keep your eyes open for Office 365 (http://www.microsoft.com/office365
). Microsoft is hosting their own Exchange/Office solution and it's incredibly inexpensive while being full-featured. However, BlackBerry support is currently in beta until January 2012, at which point it is slated to be a free add-on to Office 365. I can't wait for that to go live. The Office 365/BlackBerry Cloud solution offers the most control for both Exchange and BES in a hosted package for the lowest cost.