[GUIDE] How To Enable Game Center On iPhone 3G iOS 4.2.1
1) Open Cydia and search for "GC Patcher - iPhone 3G"
this Addon from Shani allows you to enable game detection to your GameCenter and also Patches some games that got their "own" protection to check if your device is allowed to run GameCenter.
2) After connecting to your iPhone, Navigate to /private/var/stash/Applications.pwn and copy to this path the Game Center~iphone.app folder.After that, rightclick on the folder and set permissions to 0755 (755).
Make sure you select "Set group, owner and permission recursively"
3) Navigate to /system/libary/CoreServices/SpringBoard.app/
Now you got the choose between different N82AP.plist 's.
Choose the one you like from the downloaded folder and replace it with the one on the iPhone.
4) Navigate to System/Libary/LaunchDeamons/ directory then drag & drop com.apple.gamed.plist into the directory
5) Navigate to /usr/libexec/ directory then drag & drop gamed file into the directory and set the permission to 0755 (755).
6) Reboot your device, and you are done.