Sony Ericsson models:

1. Switch ON your phone without SIM Card
2. Press the left arrow once
3. Press the button * two times
4. Press the left arrow once
5. "Personalize with MNC2" will appear
6. Enter Unlock Code

Sony Models:

1. Insert an unauthorized Sim Card and turn ON your phone
2. Enter *#7465625*12*Unlock Code#

Other Sony Ericsson:

1. Turn ON your phone without Sim Card
2. Press left arrow ONE TIME
3. Press * button TWO TIME
4. Press left arrow ONE TIME
5. The message "Personalize with MNC2" will appear
6. Enter Unlock Code.  It may be necessary to PRESS ENTER or OK