multi-person PM thread view?

[whodah]

heya!

i'm finding a need for people to be able to PM multiple people (which vB can do) but to display it as if it were a post that only those 'invited' or PM'ed can view...

i.e. when user1 PM's user2, user3, and user4, it starts a 'thread' that only user1, user2, user3, and user4 can view.

thus when any of the three users 'reply' or 'post', all the other users can see it too rather than replying on them to 'reply all' on a PM...

does anything like this exist? i've searched, but have no idea what keywords to use for something like this, heh!

thanks!!