Nope, not MSM.
The Dash has a separate application called "Instant Messenging" On its opening screen you are given 3 choices -- AOL, ICQ, and Yahoo!.
I did some more research and found that evidently when you use this app, T-Mobile charges you an SMS fee for each IM (shocking, isn't it! :wink: ).
I know from my PocketPC days there are some IM programs that rely on SMS and others use just regular data. Since an SMS-fee attached to every IM could really add up, I think I'll try installing Agile Messenger since I believe that one uses data, not SMS, and it's FREE :P
http://www.agilemobile.com/downloads.html