Now here is a new hack that might just give you the features of latest iPhone in an old or obsolete iPhone.
There is a new hack called Whited00r that allows iOS 5 features to be installed on the original iPhone and iPhone 3G devices.
Not only that, Whited00r also works in the early iPod touch models.
Whited00r will automatically jailbreak your device, and the latest version of Cydia, 1.1.3, will be installed on it. The biggest advantage of the tool, is that you will get true multitasking, and apps will keep in running state in the background.
It is as simple as running a manual IPSW install via iTunes before Whited00r takes over and installs a custom iOS firmware package. Apparently you will be running a heavily modified iOS 3.1.3 IPSW. iOS 3.1.3 IPSW is required on older iOS devices. This version of iOS comes with a custom iCloud setup. It does not include the new Notification Center included in iOS 5.