In Outlook 2010, you can have multiple exchange accounts and therefore multiple calendars.
How can I sync up calendars between the two Exchange accounts I have in Outlook 2010?
The beauty of calendaring in Outlook 2010 is that you don't have to sync the calendars. Instead, you can sync multiple accounts, and overlay (or side-by-side) the calendars of your choice. Since you're in true "multiple account" mode, all calendars are fully available offline, as well!
If you want to get the calendars to a mobile device, things get a little different. All the major players now let you sync multiple Exchange accounts just like Outlook, but iOS is the only one that supports multiple calendars within a given account. The others (I've tested WebOS, Windows Phone 7, and Android 2.2) sync only the primary calendar for the exchange account.
You would have to merge them. You can email your calendar in ICS format. Then use that file to merge it into the other calendar.
Or you could just give both Exchange calendars share permissions to each other's calendars.