A student from the University of London, Florian Kraeutli, has been working on such a possibility with an iPhone 4 with jailbreak . The phone’s accelerometer records both the intensity and the frequency of the vibration, and maps these measurements to an on-screen keyboard.
The system requires training , as we can see in the video, as the different surfaces on which we put our phone will behave differently depending on how we tap them with our fingers. Florian claims to have achieved around 80% accuracy, which, although not enough for typing, is still a high percentage for sensors not designed for that purpose. If we used an accelerometer more accurately, or perhaps used several, and improvements in predictive text dictionaries we could be able to type anywhere in the future.