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OmniFocus for iPhone exports information to the Calendar application as a way of making alerts/reminders possible, but it's one-way. OmniFocus doesn't attempt to do a two-way sync.

OmniFocus for Mac does sync with the ToDo portion of iCal, but the feature is a holdover from the pre-iPhone days; it was intended to help you get your to-dos onto your Treo or similar.

As far as I know, there aren't any apps out there that will sync the ToDo database on your Mac with an iPhone. (The calendar app on the phone does not interact with the ToDo database.)