Apple has not released the information on the iOS 5 feature page about the limitations on legacy hardware, but the technical community who already has access to beta versions of iOS have begun to discover which features will and wont make it to the iPhone 3GS.
Check out the demonstration of the iPhone 3GS running iOS 5 in the video which follows :
Note that the device in the demonstation is running the first beta of iOS 5, over the period of testing, Apple has released seven beta builds and in the past Apple has removed features which they have introduced in earlier beta builds.
- Notification Center - The biggest improvement to iOS since it's inception is the notification center. Having taken a lesson from Android, iOS 5 features a notification center which can be brought up by swiping down from the top of your iPhone. This feature will be available.
- Twitter Integration - Twitter has been tightly integrated into iOS 5 and this also will be available.
- Newsstand - The Newsstand application allows you to manage you magazine subscriptions directly from your iOS device. This app will be available.
- Camera App - The Camera application will feature grid lines and allow you to lock the exposure and brightness settings, but you will not be able to edit (red eye removal, crop, magic wand) your image.
- Safari App - While the 3GS supports Reading Lists, the new tab bar which appears below the address bar along with the Reader feature are not available.