A method for using a memory area of a mobile communication terminal is disclosed. The method is directed toward managing a personal information manager (PIM) in a mobile telecommunication phone. A memory area is assigned to each field and an index number is designated according to a type of data in the memory area. For inputting data in a memory area, the user inputs data in a memory, searches for existence of a corresponding index of the entered data, and updates the relevant data based on the search result. The useable area of memory is thus expanded and more efficiently used by classifying available memory areas and designating an index number to each field.