According to this PC World article, come next Tuesday, any third party Twitter apps that require a user name and password to login will no longer be usable with Twitter's service.
I sincerely hope RIM is working on a new version of their Twitter for BlackBerry app that is compatible with the Oauth login.
Any App that uses the OLD authentication process will be useless. As far as I know BlackBerry Twitter App already uses OAuth so there shouldn't be a problem
The old authentication was turned off on 8/31, so if the app you're using still works then you're good. As long as you have the newest version of T4BB, you should be good.