This functionality might not (yet) be integrated into OmniFocus for Mac (and iPhone), but there is a solution for syncing via WLAN in your home/office network.
It's a little something for techies, but if you're not afraid of a config file:
http://forums.omnigroup.com/showthread.php?t=9114
or directly:
http://manas.tungare.name/blog/2008/...cus-to-iphone/
Regards
Boris