The Calendar app in iPhone OS 2.x could be synced with iCal using two methods. First, using iTunes, both personal and read-only subscribed calendars could be synced between your Mac to the iPhone. With this method, you were able to select which calendars you wanted to sync and which ones you didn’t. Second, you could sync with MobileMe. This method gave you instant push updating between iCal calendars and Calendar on the iPhone.
A step-by-step guide to escaping calendar confusion