For both HDR and GameCenter

 You will need to be jailbroken on the iOS 4.1 firmware to continue.

There is no Game Center application on the iPhone 3G! You have to copy it the Game Center App by yourself to get Game Center working. This just enables the function! Enables HDR images in the camera app for the iPhone 3G and the iPhone 3Gs and GameCenter for the iPhone 3G via WinterBoard. Please note: This package has 3 things to enable. HDR, GameCenter and both. Don't use HDR and the GameCenter enabler, because it won't work. Use the 3rd enabler (HDR/GameCenter enabler) for both.

Step One
Press to launch Cydia from your Springboard.



Step Two
Press the Sections tab at the bottom of the screen.



Step Three
Press to select Tweaks from the list of Sections.



Step Four
Press to choose HDR/GameCenter Enabler from the list of Packages.



Step Five
Press the Install button at the top right of the screen.



Step Six
Press the Confirm button to begin installation.

Step Seven
Once installation has completed successfully click the large Reboot Device button.




Only for HDR Photos

First of all, you have to know what the hell you’re doing, if you don’t, don’t attempt it. Once the information is live, there will probably be a Cydia package that pops up sooner or later that will do it for you, just be patient. This is also only for iOS 4.1, enabling HDR on <4.1 isn’t possible, at least not at this time.
Your device must be jailbroken with OpenSSH installed to do this procedure

1. Make sure you have installed OpenSSH through Cydia. When it’s installed, SSH into your device (I recommend you also use the “passwd” command to change your password from the default “alpine”)
2. If you have an iPhone 3G, grab the file located at /System/Library/CoreServices/SpringBoard.app/N82AP.plist
3. If you have an iPhone 3GS, grab the file located at /System/Library/CoreServices/SpringBoard.app/N88AP.plist
4. Add a key named “hdr-image-capture” with a boolean value of “true” to the “capabilities” section of this property list
5. Save it, and use SSH to replace the copy on the device with your modified version
6. Restart SpringBoard, or just reboot your device. You should now have access to the HDR setting in the camera application.

Shout out to Will for finding this, although, there are easier ways to film higher quality porn, homie. You should really just pick up an iPhone 4 as I’ve been telling you, it has a much better camera.
Sidebar: No, iOS 4.1 doesn’t have a jailbreak out yet, so don’t ask me for it; I’m simply informing you of the steps for when the jailbreak is released.