*#06#
for checking the IMEI (International Mobile Equipment Identity)

>*<<*<* for checking the firmware revision information (software release) >*<<*<*>
1-row text strings. if pressing yes you can check the phones text programming in currently selected language.

>*<<*<*>>
n-row text strings. if pressing yes you can check the phones text programming in currently selected language.

The Service Provider (SP) Lock
The Service Provider (SP) Lock menu is used to lock the cell phone to the SP's SIM card. Once the cell phone is locked to a specific operator, if one inserts a SIM card from a different operator the phone will refuse to accept it! The cell phone will however accept another SIM car from the same operator.
To activate/deactivate this lock one needs a special secret code that is not available to the end user.

Name:  Sony Ericsson T28 Secret code.jpg
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Here is how to activate the menu:
<**< Lock to Network? if pressing yes you have 5 attempts to enter NCK.
<**<< Lock to Network subset? if pressing yes you have 5 attempts to enter NSCK.
Warning: Your phone can be locked to a service provider FOREVER by doing this! If an invalid code is entered all five times, the menu will exit and be deactivated! Any further attempt to activate the NCK/NSCK lock Menu will result in the response "Not allowed"! However the NCK/NSCK lock can be recover through a direct clearing in the EEPROM.

Shortcut for Last Dialed call menu
If you for some reason don't want to enter the 'Last Dialed calls menu' by using the 'YES' key you can use the following key
stroke instead: First '0' then '#'.