Yup, got both phones, I use two contracts so luckily I do not have to go through your dilema
I really do not know which to choose
The camera on the W800i is better for still photos, especially in low light conditions, but, the movie recording on the D600 is miles better than that of the W800i.
General usage, I feel the Sony Ericsson is still more intuitive, and you can certainly get more software (like java games for example) that are compatible with the W800i, and you do get that 512MB memory stick too which is worth quite a bit in itself. But the D600 counters with a fantastic screen, superb build and material quality, and much much nicer looks, the piano black screen surround is particularly fetching.
The loudspeaker on the D600 is also better than the one on the W800i, more dynamic, but, it's mic is useless at a distance, I called the wife and had the phone less than 2ft away with the handsfree speaker mode enabled and she could barely hear me, the W800i mic is much better for this, even if the speaker loses out a little on dynamic ability.
So, all in all, they are both pretty even, it will be a hard decision

, and I for one can't really choose between them
