Model : Nec N342i

1 - Switch ON your phone without SIM Card,
2 - Compose : **00012*CODE#.

Model : All others NEC

1 - Switch ON your phone without SIM Card,
2 - Compose : #7320*CODE#.

Model : old NEC

1 - Switch ON your phone without SIM Card,
2 - Compose : #3210*CODE# and press Call Button.