A new technique to enter text using a mobile phone keypad, Less-Tap, is described. The traditional touch-tone phone keypad is ambiguous for text input because each button encodes 3 or 4 letters. As in Multitap, our method requires the user to press buttons repeatedly to get a required letter. However, in Less-Tap, letters are rearranged within each button according to their frequency. This way, the most common letters require only one key press.
Unlike dictionary based methods, Less-Tap facilitates the entry of arbitrary words. Unlike LetterWise and T9, Less-Tap allows entering text without having to visually verify the result, after some initial training. For English, Less-Tap requires an average of 1.5266 keystrokes per character (vs. 2.0342 in Multitap).
We conducted a user study to compare Less-Tap against Multitap. Each participant had three 20-minute sessions with each technique. The mean entry speed was 9.5% higher with the new technique.