The following is a step by step guide to unlock T-Mobile Samsung Galaxy S (Vibrant 4G) to use on All GSM carriers including AT&T. I have verified every step on both Android Froyo and it had worked for me. It should work for you too. This is the easiest method i've found and it does not require you type or modify files manually. So it's safest and you will be unlikely to brick the phone.
- Check whether your phone is already unlocked or not. Follow the steps in my previous post.
- If it is not unlocked. Download and install InfuseRootUnlock_V4.zip (Windows/Linux Only)
- Enable the USB debugging mode on the phone in Settings -> Applications -> Development -> USB Debugging
- Connect the phone to PC via USB and run the root.bat file
- It should root the phone and output a unlock code in the console. Take down the unlock code.
- Now disconnect the phone and insert your Non-T-Mobile sim card (AT&T sim card for example)
- Reboot the phone and it should ask for your network unlock code. Input the code obtained from step #6 and confirm.
- Now your phone should be unlocked. You can verify whether the phone is unlocked with steps described in #1.
Note: If the anything goes wrong. You may hard reset the T-Mobile Samsung Galaxy S 4G and start over.
Leave a comment if it works for you!