There are few methods in tracing and mapping the keypad layout on a mobile phones keypads on printed circuit board. One of this quick and very easy method is by using an schematic diagram, if that certain mobile phones have available unto it. Schematic diagram is very useful guide in every aspects of hardware troubleshooting.
Now assuming that you already have knowledge how to use and read it, follow this simple steps below.
Browse to bottom of the pages where yo can locate and find like the picture below., it is the keypad circuit section. In that schematic layout you will notice that each corresponding key characters is being group into lines. This group of keypad switch lines is being marked with rows and columns.