I got this code on ebay, it unlocked my Samsung G600 but it reset imei number to zeros ! 

I wouldn't recomend using as it may have destroyed my phone

*2767*3855#

Instructions:-

Power phone of and then power back on. (Without Sim card).
Then at "inset sim" screen enter the code above exactly how it
appears above.
Then power phone off take battery out and replace sim with
alternative sim card.
Your handset should now be unlocked.
If this doesnt work:-

Unlock Code
#*7337#

Entering Code Instructions
1. Take out the SIM card from the phone and switch the phone on.
2. Enter the unlock code into your handset.
3. Now replace your SIM card and turn the phone on.
4. Your handset should now be unlocked.


Alternative Solution if the above fails.

Unlock Codes
Code 1: *7465625*28782#
Code 2: *7465625*28638#

Entering Code Instructions
1. Remove SIM card from handset
2. Enter Code 1 into the handset
( Your handset will display " auto subset lock activated" )
3. Enter Code 2 into handset
4. Your handset should now be unlocked.

a) Enter an alternative network SIM card into your Samsung and reboot.
b) The new network should be displayed in handset window.
c) If the process is repeated with yet another alternative network SIM
card, you may be requested to input a security or pin code to enable
the use of the new SIM card.
d) Enter 00000000 (8 zeros) which should enable the SIM to be accepted.
e) Finally once again enter 00000000( 8 zeros) and this should
permanently unlock the Samsung.


Final alternative Solution if the above fails

Unlock Code
#7465625*638*7337#

Entering Code Instructions
1.Take out the SIM card from the phone and switch the phone on.
2.Enter the unlock code into handset.
3.Now replace your Sim card and turn the phone on.
4. Your handset should now be unlocked.