Here are some useful codes for Sony phones...

*#06# -> Displays imei
*#7465625*12*xxxxxxxx# -> where xxxxxxxx is the unlock code
*#7465625*XX*xxxxxxxx# -> where xxxxxxxx is sim code
XX can be:
12 for NCK lock
22 for Provider Lock
32 for Network Lock
42 for SIM code Lock
52 for Subset Lock
62 for Corporate Lock
72 for IMSI Personal
99 for IMSI Range
*#9275625*11*xxxxxxxx# -> where xxxxxxxx is Wap code
*#00xx# -> Changes Language (xx is your country code)
*#0000000# -> Resets Language to auto-selection
*#7465625 -> Displays SIM Lock Status
*#7353273# -> Displays Firmware Version
*#78737322867973738# -> Super Factory Reset
*#73287489263373738# -> Resets Security Code to 0000
*09*(PIN Code)# -> Turns PIN Code On
#09*(PIN Code)# -> Turns PIN Code Off