The Controls on the Top Edge of Your iPhone
Depending on what iPhone version you have, it has certain controls on its top. All iPhones include a headset jack and a sleep-wake button. The iPhone 3 and 3GS also feature the SIM card tray, and the iPhone 4 includes a microphone:
Headset jack: Plug in the iPhone headset that is included with your iPhone. That headset looks a lot like white iPod earbuds. Unlike the iPod earbuds, however, the iPhone headset has a microphone so that you can talk as well as listen.
The headset jack on the original iPhone is recessed, so most third-party earphones (such as those made by Shure, Etymotic, and Future Sonics) won’t work with it. However, from companies such as Belkin, you can buy an adapter (starting at around $11) that enables you to use just about any brand or style of earphones you like with your iPhone. Fortunately, Apple listened to customers. The iPhone 3G, 3GS, and 4 don’t have a recessed headset jack and don’t require an adapter.
Microphone (iPhone 4 only): Used for FaceTime calls and noise suppression during phone calls.
SIM card tray (iPhone 3G/3GS only): Where you remove or replace the SIM card inside your iPhone. (The SIM card tray is on the side in the iPhone 4.)
Sleep/wake button: This button is used to lock or unlock your iPhone and to turn your iPhone on or off. When your iPhone is locked, you can still receive calls and text messages, but nothing happens if you touch its screen. When your iPhone is turned off, all incoming calls go directly to voicemail.