A fairly reputable source claims that Apple is testing three different hardware designs for the next-generation iPhone. One potential model is rumored to be similar to the current iPhone 4, but with the usual spec bump, including an improved battery and camera. Another possible design (however unlikely) includes a slide-out keyboard.
Apple is, without a doubt, testing many different configurations for upcoming hardware, most of which will never see the light of day. A slide out keyboard would seem silly on a mobile iDevice, considering the accuracy of the virtual keypad. A device with external moving parts is not Apple’s style, and unless something terrible happens to Jony Ive, it’s not likely that we will ever see an iPhone with a physical keypad.