There's certainly no need to redirect. Simply serve different content. That is, no need to waste time and resources on a redirect to another page, when the server can respond directly with appropriate content.
Depending on the nature of the particular page, and the target device, this can be as simple as substituting a different style sheet. Let's take the case of simple articles, with no pictures. In your case, though, since apparently the Blackberry doesn't support CSS (or, doesn't by default) it won't be quite so simple. So, you'd want to reformat the article for the Blackberry's screen. Perhaps break it into pages the size of a Blackberry screen. That even is probably more than necessary, as by default text flows to the width of the screen, and vertical scrolling is easy and expected by users. Certainly, any multiple-column or fixed-width layout must go, though!
While you can't use CSS, if you use a CMS on the server end, you may be able to simply write a different server-side template for article presentation on the Blackberry.
In the case of images, you may want to have lower-resolution images that are substituted for the full-resolution ones. Or, this might be done on the fly using something like Image:Magik. Or skip the images.
Maybe your users won't want to read articles on their Blackberry. You may have some particular interactive feature (say, for example, airline flight delays) that is of particular interest to them. They probably aren't interested in reading about how to pack when they are already in the cab stuck in traffic on their way to the airport. So, make sure you that feature is clearly featured on the home page for your Blackberry users, and make sure that the lookup form that you serve them is optimized for the Blackberry screen.
I'm assuming that there's something uniquely appealing about the Blackberry device to your users. Otherwise, your efforts might best be directed toward more general optimization for mobile devices.