The iPhone’s home button is more functional than you think – it’s not just there to take you back to the home page.
iPhone Home Button Trick 1
There is a common misconception that you must press the "Sleep/Wake" button to bring your iPhone out of sleep mode. You can press either your home button or your sleep/wake button to wake your sleeping iPhone and bring up the "Slide to unlock" screen.
iPhone Home Button Trick 2
You can assign several functions to "double-clicking" your Home button. Simply go to Settings -> General -> Home Button. You should arrive at this menu:
You can choose whether double clicking your iPhone takes you to your "Favorite" contacts, or brings up iPod controls. While phone favorites is convenient, setting it to iPod mode allows you to start music no matter what else you’re doing. In other words, it brings up iPod controls (play, pause, skip, volume) over whatever other application you are running (Safari included).
Setting iPod Controls to "On" means that if you already have music playing, double clicking the Home button will bring up iPod controls even if you have the Home Button set to "phone favorites".
iPhone Home Button Trick 3
Double clicking the home button from the "Slide to unlock" screen will always bring up iPod controls, right over the "Slide to unlock" screen. You can control your iPod without even unlocking your phone!