I recall seeing where 3.0 would support subscribed calendars. I've subscribed to my wife's iCal calendars long ago and they show up on iCal. However, they are still not on my iPhone with 3.0. Wasn't that supposed to be a feature?
Wirelessly posted (iPhone 3G (white): Mozilla/5.0 (iPhone; U; CPU iPhone OS 3_0 like Mac OS X; en-us) AppleWebKit/528.18 (KHTML, like Gecko) Version/4.0 Mobile/7A341 Safari/528.16)
You have to add them as new/separate accounts. In Settings, add a new mail account, choose "Other" for the type, and you'll see subscribed calendars at the bottom of the list.