Depending on if you want to install the software on your Excahange server or at your workstation, Advantage International, Inc. has developed two solutions that will enable you to sync your Blackberry to your Outlook Public folders.
Add2Exchange for Calendars™ is an Exchange add-on, enterprise-wide Outlook calendaring synchronization application which synchronizes any combination of Outlook calendars - private (mailbox) and public (group/global). This application works with any PDA (cradled/wireless) or Smartphone and Outlook Web Access.
P2P Calendar Synchronizer™ (P2P) is an Outlook add-in for Exchange users which auto duplicates and synchronizes Outlook calendar appointments created in a public (group/global) calendar to a private (mailbox) and ready to synchronize to a PDA (cradled/wireless) or Smartphone.
Fully functional free trial versions available for download at www.diditbetter.com