I know about Chapura pocketMirror as i had setup another client with Treo Sync longtime back.
I have another client with same requirements - access to shared calendar.
I set them up with a Shared Calendar solution outside exchange for their blackberries.
a) Create a google account for the company
b) Download Google Calendar Sync tool
http://dl.google.com/googlecalendarsync/GoogleCalendarSync_Installer.exeConfigure this tool with the company account in step-1 above.
c) This tool will sync local outlook to the web-based google calendar every 120 mins by default (you can configure this and reduce minutes to 5-10 mins)
d) Download GCalendarSync on your SmartPhone - blackberry etc.
Setup your blackberry with the same company account.
http://www.google.com/support/calendar/bin/answer.py?hl=en&answer=89955-----
since you have already setup a particular user's calendar to be used as a shared calendar, you can setup a Google Calendar account to sync with this.
And then download the calendar items on your phone using GCalendarSync.
This is not a microsoft solution :-)
let me know if this works.