Hi ,
GAE XMPP documentation states that is not possible to set status message for an app ( https://code.google.com/appengine/docs/python/xmpp/overview.html#Google_Talk_User_Status ).
On other hand, I've vark IM client has status message set. Obviously it is not hosted on GAE, but it is possible to set status message for app.
I have to dig under the hood, but wonder it there are any python references regarding this topic ?