I've begun work on XEMPIM, a complete re-implementation or EMPIM in Objective C/Cocoa for Mac OS X.
It's coming along quite well, the core classes are mostly written and I'm starting in on jaContacts.
Once the project grows a bit, I'll post stuff.
EMPIM 0.1 has now been released!
Availble are source tarballs of:
EMPIM (with the jaContacts module)
EMPIM (with no modules)
and just the jaContacts modules