Last post of the year 2011!
The following is a step by step guide to unlock AT&T Samsung Galaxy S2 (Attain) to use on All GSM carriers including T-Mobile. It is fairly long process but I have verified every step on Android 2.3.4 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 here.
- Check whether Your Samsung Galaxy S2 is on Android 2.3.4. You may find it in the Settings->About Phone menu. If not, please restore to the stock rom 2.3.4 in order to root the phone. You may follow this guide to restore to stock rom.
- If it is not unlocked. Download and install superoneclick to root the phone. You can download the tool from here.
- Now go to Marketplace download and install the busybox Installer by Stericson. Run it to install busybox.
- Now go to Marketplace download and install the app Galaxy_S Unlock by Helroz. Follow the steps in the app to unlock.
Note: If the anything goes wrong. You may hard reset the AT&T Samsung Galaxy S2 and start over.
Leave a comment if it works for you!