An alphanumeric data input system for entering text into portable electronic devices by making linear traces or taps with a thumb or finger on a touch sensitive lineographic keypad. This keypad is conveniently located on the upper and left part of the electronic device in order to facilitate the natural motion of the thumb thus avoiding fatigue and strain of the same. The system allows the user to enter operational commands on the keypad, as well as entering of letters of different alphabets such as the Latin Alphabet, Mathematical Greek and Russian Alphabets and possibly of alphabets of other foreign languages including Japanese, Chinese and Korean. This system can be used for entering a combination of letters to speed up the writing process, and enables the entering of punctuation marks, typographical symbols and a wide range of mathematical symbols.