I hate to say it
BlackBerry have a point - the keyboard looks uncannily like the one on my old, abandoned, work BlackBerry Bold, down to the use of opposed curved ridges on each half of the keyboard. Whether this is a legitimately patentable design, I am no patent lawyer (thankfully) but I've seen lots more flimsy patents.
If one of BB's strengths is its keyboard, then perhaps they should be selling this sort of thing themselves already and let people use a genuine BB keyboard without having to put up with the rest of the BB. If only they had the spare cash to simply buy Typo.
Have to say though that the iPhone 5(s) form factor doesn't really lend itself to this type of add on - looks impossibly tall with it on.