The iPhone has been around for nearly four years. And in that time, millions of people have bought and used iPhones, swiping and tapping their way through life. Most of those people believe they know how the iPhone works.

But dig a little deeper into the iPhone’s latest operating system, iOS 4.3 — available for the iPhone 3GS and the AT&T iPhone 4 — and there’s another layer to master. (Sorry, Android users, but that OS has so many versions and skins that a quick guide would be neither very quick nor much of a guide.) Beyond the realm of those basic iPhone controls is an advanced level of shortcuts and tweaks, some of which even hard-core users may not know exist.

DOUBLE-TAP Even while your iPhone is locked, you can access the audio controls by double-tapping on the home button when the lock screen appears. This saves you the time it takes to unlock your phone, open a music-playing app like iPod and get to the volume and track controls. This feature is not limited to Apple’s iPod app. If you are using Pandora, for example, the same technique will bring up its controls.

VOICE ACCESS If you press and hold the home button while the phone is locked, you can still access Voice Control to place a phone call (or FaceTime call) or get to any of the iPhone’s other voice commands.