The range of modes of communication for mobile devices is rapidly expanding. Smart mobile telephones can already deal with voice (both human and automated), text (also both human- and computer-generated), visual material (both the delivery of photographs and videos to mobile devices and the capture and transmission of such images from the device), spatial position (e.g., GPS), motion (using built-in accelerometers), and a host of other input and output modes enabled through add-on hardware or software apps. Apps are already available (for example) to convert voice messages to text, and vice versa.