Even though the iPhone 5 is quickly becoming the iPhone of choice these days, there are still plenty of good cases for the iPhone 4 and 4S -- including those with keyboards. The Boxwave Keyboard Buddy Case has been out for nearly two years, and they've added a US$79.99 (on sale from $89.99) version that includes a backlit keyboard for use in low-lit areas. I tried it on my 4S for a couple of days, and while it's a solid case, it's not one I'd use unless I absolutely needed to have a keyboard.
The case is made of molded plastic and is quite a bit thicker than the normal iPhone case to accommodate the keyboard, but not as bulky as one would think. It's only slightly thicker to me than when I had an Otterbox case on my iPhone. It features a sliding keyboard that allows you to type in landscape mode and includes a micro-USB cable for charging.
Here's where the design flaws start to come in. To keep the overall case as thin as possible, the keyboard is so thin that it makes the entire case top-heavy when you're trying to use it. When the case is closed, you can still wiggle the keyboard instead of having it locked in place. If you've got your phone tossed in a bag, I can see the keyboard slider coming out without you realizing it.
The case has a secure fit on the phone -- a little too secure, I found out, when I tried removing it after the review. It required excessive force on the back of the iPhone right over the camera lens and it took a good five minutes of pushing from the back and prying the sides away before the case came off.