Newer Sony Models (Xperia Range)
Most new Sony will ask for the unlock code when you put a sim in it wont yet accept because it is locked.
When you receive your unlock code(s) they will look similar to the example below:
Your unlock code is :
The letters CCK, NCK, NSCK, SPCK indicate which code to use the different locks on your handset.
So you need to find out which lock is active on the handset ( But usually you'll only need the one marked NCK).
To do this you need to look in a secret menu on the phone
Tap the following in as if you were dialing a number to make phone a call...
A new hidden menu will appear.
Tap on service info
Tap on SIM lock
If you have [x] Network 5 - this means your phone needs the net NCK Code
If you have [x] Service provider 5 - this means your phone needs the SPCK Code
Other Models: 99% Sony Ericsson
1 - Switch ON your phone without SIM Card,
2 - Press 1 time the left arrow,
3 - Press 2 times the button * ,
4 - Press 1 time the left arrow,
5 - The message 'Personalize with MNC2' will appear,
6 - You can now enter the Unlock Code we send to you.
If your phone have a 'JogDial' (ex : Sony Ericsson K700i) you must press 'Down Arrow' instead of 'Left Arrow' for step 2 & 3. We mean by 'Down Arrow' to direct the JogDial down !
W950 models need to use * up * down ** down (up/down using the jog dial on the side).
Enter # p w + CODE + 1 # into your phone.
Tap repeatedly the star key to get p w + symbols
1. Insert a Non accepted SIM card ( EG your new SIM)
2. Switch the phone on
3. Press Left * * Left ( Left is move JogDial stick left )
4. This will open a hidden menu with 4 options (See image)
5. Select 'Network' ( You should see a locked padlock next to the option )
6. Enter the unlocking code we sent you. ( The one marked NCK )