1. A mobile communication terminal, comprising: a key input unit having a plurality of keys; a display unit; and a controller configured to display a plurality of variable-related applications corresponding to a type of variable input through the key input unit on a display unit, and to input the input variable in a predetermined input field of an application selected from the plurality of variable-related applications, wherein the input variable is provided in a different form according to the selected application, and wherein different forms of the input variable include at least two of a mathematical operand, a time, a date, and a receiver number.