Network locks are a way for carriers to ensure subscribers finish up with their contracts (networks can easily block the IMEI of handsets that belong to delinquent accounts). However, having your phone opened to other networks does have its benefits. For example, if you’re traveling abroad, you can avoid hefty roaming charges by buying prepaid SIM cards.
Samsung’s flagship Galaxy S3 is usually released in the U.S. on-contract, which means it will be locked to your carrier. While some carriers will allow network unlocking for a charge, enthusiasts would usually be able to do an unlock through free means. On the XDA Developers forum, user zohawkish released a free unlocking tool that would render your Galaxy S3 “open line.”
First you need to backup your “EFS FILE” in safe place.
you must be in unlocked stock firmware like BLG8 (using voodoo app + libsec-ril.so (mike1986 fix))
unzip the attached zip “efs.zip”
copy the files (.nv_core.bak, .nv_core.bak.md5) to your EFS file
reboot and enjoy !!!
As of this writing, though, the original post had been pulled down. Zohawkish pulled out support for the unlock tool given complications that have arisen, particularly with the need to backup EFS and restore the backed-up EFS if a user wants to update to future Jelly Bean releases.
In short, is it worth the trouble to unlock your phone at this point?