Ah, looks like it is possible, thanks!
I'm actually now looking at BusyContacts instead, as it's a $50 purchase instead of a $57/year software rental.
(And no, I'm not talking about syncing with someone else's computer, I'm talking about syncing between my own two Macs and my iPhone.)
BusyContacts (and BusyCal) are on sale until 11/30. I might grab both.