Owners of the Samsung Galaxy S and its variants including the Captivate and the Vibrant take note. The folks on xda-developers discovered much to their surprise that unlock codes for the Android handset are stored covertly on handset. Rather than on some remote server under lock and key, the unlock code is stored in a .BAK file on the internal SD card.
All you need to do is mount your Samsung handset via USB, drag the file onto your desktop, and run a script to extract the unlock code. Too easy for you? You can up your geek cred by using a hex editor to locate the code yourself. Too hard for you? You can cough up $10 and download the Galaxy S Sim Unlocker from the Android market which will extract the code automatically for you.
The unlock code opens up the door to the possibility of running a T-Mobile Vibrant on AT&T’s 3G network and an AT&T Captivate on T-Mobile’s network, though the Captivate reportedly only connected via EDGE. Good news! If you have to return a handset for warranty purposes, you are fortunate as the process does not require you to root your phone and the handset can be re-locked with minimal effort. All the detailed steps can be found here at xda-developers where there is ample support and conversation to help you navigate the process.