A MM/MH Messenger

I thought about this where its a messenger basically like Yahoo or MSN but just for MM and MH members.

It works the same way you can add people to your own personall list and so on, the setup of the look of the messenger would look just like the site.

As far as bandwidth, I wonder If it would count towards "extra" bandwidth for the site or not

Basically yes it would use bandwidth, however it depends on how it would be set up.