Techniques for fast and easy mobile text-entry with three-keys

SMS (short messaging service) has become extremely popular in Europe. It allows users to send and receive short asynchronous messages at low cost. Text-messaging requires text-entry facilities, usually awkward and small 12-key phone keyboards labelled with the alphabet in the classic phone-layout. As devices are becoming smaller, for example wristwatches with Internet connectivity, there is less space for keys. Researchers have experimented with three-key text input devices and come up with designs allowing text to be entered with nearly as few as 4 keystrokes per characters on average. However, experiments have shown that these interfaces are hard to learn and thus slow to use in practice. In this paper we study four three-key mobile text-entry strategies with different characteristics, namely multiring, three-based binary and multitap. Three of the methods require from 1 to 7 keystrokes per character, and the third method always retrieves the required character with a constant of only three keystrokes per character for English text. Experiments are used to demonstrate that the techniques are easy to learn and pleasant to use. The techniques are cheap and simple to implement and therefore hold great potential for future text-enabled consumer electronics.