Apple hasn’t provided support for HDR photography on their older 3GS and 3G iPhones with iOS 4.1. However with a few small tweaks to a jailbroken iPhone can enable it for you.
Remdmond Pie has put together a great guide on how to enable HDR option in older firmware versions via SSHing and editing some files. You can read the full walk through here.
Before your follow the guide, make sure you have a jailbroken iPhone 3GS or an iPhone 3G, complete guides for jailbreaking both the devices can be found here and here respectively on the Remond Pie website.
** Updated 16th September : there is now a HDR Enabler App available that makes it even easier to enable HDR on your 3g or 3GS iPhoneFiled Under: Apple iPhone