If you’re using an older device that doesn’t support multi-tasking, you can quit an application manually, though this also works as a force quit on the newer devices if you prefer. You’ll need to follow the following steps:

  • Hold down the Sleep/Wake Button on the top.
  • Wait for a red slider to appear. Don’t slide it.
  • Let go of the Sleep/Wake Button.
  • Hold down the home button and the app will force quit.
  • Once you’re back on the home screen the application should be closed, and you can re-open it normally again.

Note:
Works on iPhone 3G/3GS/iPhone 4