Since I have seen alot of threads started about this subject I figured I would post here about my findings. I have read and read and read all over the interweb about getting the promised unification to work. Mine, like others, is not working as promised. I am running Mountain Lion and iOS6 beta 3 and I have tried the toggling on/off of iMessage on my iPhone and the computer and adding my number to my Apple ID on the Apple support page. None of which added up to this feature working as described in the Keynote speech which I figured it would in Mountain Lion. So I figured I would give Apple a call and have them trouble shoot this with me to see what I did wrong. Well according to Ben at Apple "the unification feature has not been implemented yet." And he has not been told when we can expect the feature to begin working. So to those who have gotten it to work as described in the Keynote consider yourself lucky or one that fell through the cracks.