The D-807 is supposed to drop in the second quarter of this year. It appears to be just a quad band version of the D-800. It may be pretty hard to find, because outside of Cingular in the US, nobody else uses the 850 band. The D-800 adds WMA playback, and has EDGE support.
The D-600 has a better resolution camera (2 MP), only supports AAC and MP3, and does not have EDGE (but I see that Samsung does have a 600E that does, if you can find one).
So, if EDGE is important you may want to wait for a few months and see if you can get your hands on a D-807. Otherwise, get the D-600.