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. 😉