A primary object of the present invention is to provide a method of automatically changing a calling mode of a telephone having a program timer installed therein as a timer setting changes, wherein the program timer comprising an on/off item responsible for controlling an on/off of the program timer, a timer setting item responsible for setting a time slot of an activation of the program timer, and a calling mode item responsible for setting a plurality of ring types, so that when the program timer is on and the time slot has been set by the timer setting item, a microprocessor of the telephone will activate the ring type set by the calling mode item for informing of an incoming call within the time slot.