I turned off Wireless Sync for all (2 - Desktop and Device Default) of my calendars (wireless sync for Device Default was off already). When I go into Desktop Manager, Backup/Restore, Advanced, it still shows all the choices that start with Calendar as greyed out. When I exit DM and check the Calendar options on my phone, Wireless Sync has been turned back on for Desktop.

I'm guessing this is because I am activated on a BES, maybe?

Regardless, I still don't see any way to delete all the entries on my Device Default calendar.