Abstract: A method of searching a telephone number is disclosed, in which when a user desires to communicate with a third party using a personal communication service unit such as a cellular phone, the user can easily dial a desired telephone number by efficiently searching telephone numbers input to the personal communication service unit. The method includes the steps of inputting a telephone number through a telephone number input means, storing the input telephone number in a memory and at the same time outputting a group of telephone numbers, which share some digits of the input telephone number, from the memory and displaying the group of telephone numbers on a display window depending on the digits of the input telephone number, and selecting at least one telephone number from the group of the telephone numbers displayed on the display window so as to dial the selected telephone number.