I don't know, if it works, but it will be nice to put also holidays into phone during the synchronization.
(If it will be possible due to phone calendar capacity)
Possibility one:
Select a holiday in MyPhoneExplorers calendar, rightclick and choose "Add holiday..."
Possibility two:
Download somewhere in the web (there are many sites for this) holidayfiles for Sunbird (*.ics) and import it in MyPhoneExplorer