You are also what mail is in the "Important," "Urgent," "Vital," "Friends" and "Family" folders.
With an Exchange email account set up in i Phone Mail (such as push Google Apps Gmail, for instance), you can have not only new messages in your default Inbox pushed to the device but changes to any folder.
You can use the stock calendar, S-Planner on Samsung phones, HTC Calendar on HTC, or Google Calendar's official app to test this.
If they work and Digi Cal don't - please send us an email with the details. Check the sync status of the phone and account, they must be all enabled to allow syncing.
If this is happening, then you may notice missing, non-existent and/or incorrect entries.
Synchronizing your Outlook (cached) address book with the Global Address book may fix these discrepancies.
In order for some GAL entries to show up properly you may need to turn off Cached Exchange Mode.