Method 1:

1 - Switch ON your Samsung Memoir with a NOT ACCEPTED SIM Card.
2 - Samsung Memoir will ask for "Password".
3 - Enter the Unlock Code.

OR (if the Samsung Memoir shows "Insert Correct SIM Card")

Method 2:

1 - Switch ON your Samsung Memoir with a NOT ACCEPTED SIM Card.
2 - Don't bother about what's being displayed on your Samsung Memoir.
3 - Compose : #0111*CODE#.

NOT ACCEPTED: We mean, to use a sim card from a network other than the network your Samsung Memoir is locked to.
CODE: Its the unique Unlock Code for your Samsung Memoir.

If method 2 does not work, you can try method 2 again but this time without any SIM card on your Samsung Memoir.