It should be possible to do this, but currently it brings in each PM seperately, as they appear in VB. However, if the subject and the sender is the same then it should be able to group them into a conversation thread.
hmm, that's a fair point actually, hadn't thought of the sent items.It's not really easy to do this, due to the way things like sent items work (which may not exist), or even just individual messages being deleted. Additionally, subjects are really the main thing you can go with and that would be nightmare to manage (and cause bad performance).
We can even reflect this merging in the inbox of both the parties. But we will have to take care of CC/BCC participants (which I have suggested in another thread).But ibnesayeed makes a good suggestion, being able to manually merge PMs into a conversation (even if its partly one sided) would be better than nothing.