An input method using standard numeric keypad which complies with CCITT standards and comprises a plurality of CCITT standard keys is disclosed. Each CCITT standard key has a corresponding CCITT key value. The method comprises the steps of: reassigning a first CCITT key value with an actuating key value of a first function; checking if the first CCITT key value is input, if "YES" then actuating the first function to reassign every CCITT key value with a new input key value of predetermined function; and, checking if any CCITT key value is input, if "YES" then performing the predetermined function corresponding to that input CCITT key value based on the first function. Therefore, all functions of the input method can be operated by using merely the CCITT standard keys without the need for other non-standard function keys.