2 calendars, 1 blackberry + BES + BB curve (cingular)
 

is this possible ? is there any 3rd party app that can do this ?

I know you can add more than 1 calender using the desktop manager. You can only add mailboxes that are already associated to your account. Such as mailboxes set under the 'Advanced' tab under your Exchange account.

The only issue with this is that you have 1 big mess of items on the calendar and can not distinguish between them on the BB. Maybe there is a program that distinguishes the 2 but I have not seen one yet.