The keypad may need to be replaced if the buttons on your phone are cracked. This guide will only instruct the user on how to replace the keypad interface, but will not actually replace the circuitry that allows the buttons to operate. Such a repair is covered in the Installing Nokia 8290 Circuit Board repair guide.
Locate the small button on the top of the phone.
Depress the button.
With your other hand, pull the front cover away from the phone.
After removing the front cover, simply peel the keypad away from the front cover