How to Turn off the Screen Rotation Lock on the iPhone
The iPhone lets you choose between viewing certain applications and content in portrait and landscape orientation. This way you can decide which orientation best suits your needs. The iPhone's rotation lock feature makes it possible for you to lock the screen in a fixed portrait position. You can enable and disable the rotation lock at any time through the mulitasking status bar.
Press the "Home" button twice. The multitasking status bar opens at the bottom of the screen.
Flick the multitasking status bar to the right reveal the iPhone's iPod controls and the rotation lock. The rotation lock icon is located to the left of the iPod controls. A small lock symbol appears on the icon when the rotation is locked.
Tap the rotation lock on. A brief "Unlocked" message appears. The small lock symbol does not show on the rotation lock icon.
Press the "Home" button to close the multitasking status bar and return to your Home screen.