BlackBerry has just released a new version of Twitter, though no important changes have been added. Actually, this is just a minor update that probably addresses some issues that have been brought in by previous versions.
As CrackBerry points out, the official changelog of Twitter 184.108.40.206 mentions that the latest update includes some bug fixes which have yet to be detailed by developers.
In addition, BlackBerry claims that SSL is now enabled by default for all communications. Other than that, there are no other improvements or new features included in the latest iteration.
Keep in mind that Twitter 4.0 is for BlackBerry Device Software 5.0 or later, Twitter 2.0 is available for BlackBerry Device Software 4.6 or later, while Twitter 1.1 is available for BlackBerry Device Software 4.5.