Good news for those users on a GSM based network wanting a Samsung Galaxy S 4G, your wish has been granted. XDA member sanfranx415 has discovered a method for finding the unlock code for these devices. Of course the method requires that the phone be rooted and lots of patience with a hex editor.
The first step to this process is copying a file to your sdcard from /dev/block/ using a terminal emulator, and then transferring it to your computer. Once that’s done the patience factor comes in, you must open the file in a hex editor and search for a certain string to locate the unlock code. While this probably sounds boring, the results are worth it if you’re wanting to use this phone on a carrier other than T-Mobile (like AT&T).
For the complete step by step guide as well as a link to an easy hex editor, visit the XDA thread.