I sent in what is (hopefully) my first working patch to the dev mailing list today.
After tracking down a few nit-picky errors, I've got my project set up so that I can update sip-communicator from cvs, update sc-avmailbox from svn, and nothing breaks!
check back in a few days and see if I'm so optimistic.
Anyway, back to work on getting an outgoing message to play. Last I checked the call to manager.createDataSource was coming back null. Since this method usually throws an exception when it messes up (IE the NoDataSourceException described earlier), I'm not even sure what that means.