documentation of the iPhone OS 3.0. You might have discovered some of them while using your iPhone 3GS but there are some features, perhaps you did not discover. Here are some of those hidden features. Take a look
1. When you attach a photo in mail, you can magnify it like you would text. Just tap and hold on the image.
2. There is no restriction in the number of apps that you can install but if the number of the apps exceed 11 screens showing 175 apps in total, then the app will be installed without an icon but you can access and use it using the spotlight search. In fact you need to use the spotlight to search the apps that are shown in more than the 5th screen for your own convenience. So, an app sans an icon wouldn’t be much of a problem.
3. You can shake the phone to undo typing. A pop up will appear when you shake the phone and you can choose whether you want to undo or keep what you have written.
4. There is an edit button when you’re inside a [text] conversation and you can now delete/forward each line in a text just like you would in mail.
5. You can adjust the song scrolling speed while listening to it. In the previous version you could only rewind or fast forward through the simple dot on the scrolling bar, but now you can drag your finger right or left to scroll through the song at high speed and if you do the movement while dragging your finger down the screen, the speed will decrease to half speed, quarter speed or fine scrubbing.
6. When bringing up the playback controls on the lock screen, it now shows song title, artist, and album. Previously it only showed the song title. The font is also smaller.
7. You can access some special characters while holding some characters down. For example while holding down the “.” sign you can get access to “…” sign. You can get quotation and apostrophes and other signs using this technique.
8. Spotlight can be accessed by swiping towards the right side of the screen or by pressing the home button while in the first Home screen page. There is a search bar at the top of mail and contact list.
9. When using the camera, if you tap on the previous photo (bottom left) and go to the flimstrip, you can select “Done” to go back to the camera. You can also zoom further into photos in the Camera Roll then you could with 2.0.
10. When moving icons on the home screen and you move an app to a different page, if you keep the icon to the edge of the page it will go on to the next page. Previously you had to move the icon away from the edge before you could keep moving it to other pages.
-- Post From My iPhone3gs