It looks like iPhone OS 3.1 enables syncing of subscribed calendars from iCal via MobileMe's over-the-air sync service. Note that this can lead to duplicate events appearing in your iPhone Calendar app if you subscribe to your OmniFocus due soon calendar on both your iPhone and on your Mac.
See this other thread for more info:
http://forums.omnigroup.com/showthread.php?t=13801
-Dennis