Many people use iPhone have become accustomed to a phone with a keypad but still miss the tactile feeling of pressing actual keys. Some manufacturers already have released an Apple iPhone 5 Bluetooth Keyboard in a case that slides out to reveal a backlit QWERTY keypad.
For iPhone 4S/4, this website talks about 7 portable keyboards for Phone 4 and 4S . Among them, the SWIVEL Bluetooth keyboard almost looks like a miniature touch screen laptop. According to the description at Concord Keystone this can be used for an iPad and iPad 2 by removing it from its case.
Just to show how it works, I referenced the following TypeTop Swivel keyboard case the You-Tube video. I suspect it works very similar to the one in from Concord Keystone.