HDR photography for iPhone 3GS and iPhone 3G wasn't something Apple provided under iOS 4.1, but that doesn't mean 3GS and 3G users have to be left out of the fun (if you're jailbroken that is).  Redmond Pie has a great guide up showing how to enable the HDR camera option provided you've jailbroken them under iOS 4.1 and aren't adverse to SSHing and editing some files.  The process really isn't that difficult, but as always, if you're not comfortable altering files on your iPhone, we don't recommend it.  So hit up the source link for a detailed walk-through.  And if you're not sure if it's worth it yet, read our take on HDR photography on the iPhone 4 or our full iOS 4.1 guide.