Add a second number to a name, From the phone book, From the start screen – Nokia 6360 User Manual

Page 54: 1 enter the phone number using the keypad, 2 press options, 3 scroll to add to name and press select, By retrieving the name, 2 press details, and then press options, 3 scroll to add number, and then press select, 5 enter the number and press ok