You get the unlock code from the carrier (or buy it from one of many places that advertise on eBay). When you put in the "foreign" SIM it'll ask for the unlock code. Put it in and the phone will be SIM-unlocked. It doesn't have to be rooted (the Android equivalent of jailbreaking).
Is there any apps that will unlock network just like ultrasn0w for iPhone? And now, I have another problem. I'm on custom rom and it stop asking to enter unlock code. I don't know how to enter the code.
Yes, I do. However, now I want to restore Stock Firmware from LG in kdz format but I can't, because I have CWM Recovery Menu installed and I can't get back to original Recovery Mode. What should I do?