May I suggest that each contributor get their own wall on their profile page. I'm thinking this might be useful if a designer wants to discuss requests etc. with a certain contributor in a way that is fair and transparent to you as our agency.
I am aware of the "comment" feature but I don't think it's the best way to contact a member.
I do think the comment feature is a good way of contacting a member, because they are notified of the message under unread comments (would this still happen with a wall?), BUT the size and location of the current "comment" button is not sufficiently dominant and easily overlooked.
For what I have read in other forums opened by buyers, I have the impresion that most of them do not know how to contact contributors. And as it was already said, the comment button is almost hidden and is very hard to find, much more difficult to realize that that is the way to get in contact with someone.