How to Check if your Sony Ericsson Xperia X10, X10i or X8 are Permanently Locked / Hard Locked?
Type the following sequence from the lock menu Sony Ericsson X10, X10i, X10 Mini, X10 Mini Pro, or X8 device
Menu => Back => Back => Menu => Back => Menu => Menu =>Back OR dial: *#*#7378423#*#* 
This works on my x10 running Android 2.3.3
Select Service Menu and SIM Lock
You will see a new menu that looks like this:

[x] network 10
[] network subset 10
[] service provider 10
[] cororate 10
[] sim 0

If there is an X beside any of the categories, then means you need specific code to unlock that phone.  
Normally, Sony Ericsson phones come only with a network lock as active.  
The most important part of this is to view the numbers beside each category. 
That number represents the number of tries you have left before your Sony Ericsson device becomes permanently hard locked to its original network carrier.  
If there is a 0 beside the category where a lock exists, then it means that your phone is hard locked.

Example 1:
    [0] Network 1
    [x] network subnet 0
    [x]service provider 0
    [x]corporate 0
    [x] Sim 0    
 This phone is locked and you still have 1 attempt to enter the Unlock Code

Example 2:
    [0] network 3
    [x] network subset 0
    [x] Service provider 0
    [x] cororate 0
    [x] sim 0
This device can be unlocked and have 3 attempts left to enter the Unlock Code

Example 3:
Sony xperia Z from nttdocom japan model (SO-02E)...
    [×] network unlimited
    [ ] network subset 0
    [ ] service provider 0
    [ ] corporrate 0
    [ ] sim 0
This device has normal network lock and can be unlocked 

Example 4:
    [0] network 7
    [ x] network subset 0
    [ x] service provider 0
    [x ] cororate 0
    [x ] sim 0
This phone still has 7 tries left to enter the Unlock Code

Example 5:
xperia ion lt28 Etc..
    [x] network 10
    [ ] network subset 0
    [ ] service provider 0
    [ ] cororate 0
    [ ] sim 0
 The [x] next to “network” means that phone is still locked Have 10 Tried Left

Example 5:
    [X] Network 0
    [] Network subset 0
    [] Service provider 0
    [] Corporate 0
    [] Sim 0
The [x] next to “network” means that your phone is locked and you have 0 tries left, so it cannot be unlocked. 
This means your device is hard-locked and cannot be unlocked by Code anymore (0 attempts left). This Need Any Software Solution to Unblock Counter,

Example 6:    
    [o] Network 0
    [x] Network Subnet 0
    [x] Service Provider 0
    [x] Corporate 0
    [x] SIM 0
This device Also hard locked and cannot be unlocked by Code anymore

Example7:
 xperia Ion lt28 when insert sim phone restart every min!
    [] network 0
    [] network subset 0
    [] service provider 0
    [] corporate 0
    [] SIM 0
This device fully unlocked there is no symbol in any of the brackets and Restart issue is not related to the lock Subject - this device is unlocked

Example 8:
    [] network 10
    [] network subset 10
    [] service provider 10
    [] cororate 10
    [] sim 0
No symbol inside any of those brackets, device is already unlocked One

Example 9:
    [] network 5
    [] network subset 5
    [] service provider 5
    [] corporate 5
    [] sim 0    
This device is Not Locked and will remain permanently unlocked even flash with custom or Any New ROM.
    
Example 10:
What if the menu looks like this?
    [?] network
    [?] network subset
    [?] service provider
    [?] cororate
    [?] sim
There is no X next to any of the menu points, it usually means phone is already unlocked.