Manually Patch Ultrasn0w 1.2.4 to Unlock iPhone 3GS on iOS 5.0.1 Baseband 6.15.00

you can try this manual method. It’s not that difficult and will give you a sense of achievement.

1. Your iPhone 3GS must already be jailbroken and installed with iPad baseband 6.15.00 (for those who had to install this baseband version). If you have baseband 5.13.04 or below, restore to iOS 5.0.1 using custom firmware which you can download from here. For newbies, there’s a full tutorial here.
2. Download CommCenterClassic (ultrasn0w patch).
3. Launch Cydia, add the following to your source and install iFile.

http://cydia.xsellize.com

4. Download i-FunBox (Windows) or DiskAid (Mac).
5. Launch i-FunBox or DiskAid and locate the following path:

raw file system/System/Library/Frameworks/CoreTelephony.framework/Support/

6. Backup CommCentreClassic file by renaming it to CommCentreClassicOld etc. and replace it with the new CommCenterClassic file you downloaded in Step 2.
7. Launch iFile on your iPhone and find the following path:

System/Library/Frameworks/CoreTelephony.framework/Support/

8. Tap on commcenterclassic, click the Blue arrow next to the file name, go to Access Permissions and set the following permissions:

• User: Read, Write, Execute
• Group: Read, Execute
  
• Global: Read, Execute

9. Launch Cydia and install ultrasn0w. Reboot iPhone.
10. Disable 3G and Cell Data Network under Settings -> General ->Network. Insert your SIM card and your iPhone should connect to your network.

Courtesy of Beijing iphone repair