Well I read over those topics and I agree with what beardie said in them.
BUT!
Some forum providers like "Enjin" have it so when you create your forums account its almost like a facebook page, and then there are the forums aswell. It has "status" updates you would add friends on the forum to see what they are saying like facebook again. I'm not sure phBB provides a feature like that, but I think something along those lines would work better for a "chat" on these forums.