Kobo for BlackBerry
In an email sent out to their customers yesterday, Kobo announced that their app will no longer be supporting BlackBerry smartphones running on an OS earlier than OS 6.0.

Dear Valued Customer,
We are constantly upgrading our apps to ensure we provide the best eReading experience. Go to the Blackberry App world today to download the latest version of the Kobo eReading app.
With this new enhancement, you may need to upgrade your Blackberry OS to 6.0 at http://www.blackberry.com/update/. Kobo will no longer be supporting apps used on earlier operating systems and we will not be able to guarantee that you can access all of your eBooks.
If you are operating an older Blackberry model and are unable to upgrade to the latest version, download the Kobo desktop app. You can be sure that all of your books will remain in your library, and you can keep reading seamlessly and effortlessly at any time.
We apologize for this inconvenience and as a loyal customer we would like to extend 25% off your next great read.
Use discount code bb25nov4US on these selected books. Expires: November 13th, 2011

To soften the blow that this may cause some users --such as those that don't have the option to upgrade to a newer OS-- Kobo is offering a 25% discount on their next purchase, but it looks like it is only valid on select titles. You can see the list at the link in the email above.