RS-232? On a ceiling fan? Ha-Ha-Ha-Ha-Ha! (Well, you could if you had a whole-house system like HomeWorks. It's just that the first thought that came to mind was a ceiling fan with a DB-9 connector:-)
Don't focus on the ceiling fan, focus on the wall switch. You will find several ceiling fan speed controls that you can control via IR and/or other protocols, such as UPB or Z-Wave.
[Link: lutron.com][Link: leviton.com]