The Controls on the Bottom Edge of Your iPhone
The bottoms edges of the different iPhone versions are pretty consistent, featuring the same controls. On the bottom of your iPhone, you’ll find the speaker, dock connector, and microphone controls:
Speaker: iPhone’s built-in speakerphone uses this speaker, and the speaker also plays audio — music or video soundtracks — if you don’t have a headset plugged in. It also plays the ringtone you hear when you receive a call.The top of an iPhone 3G or 3GS.
Dock connector: The dock connector has two purposes:
You can use it to recharge your iPhone’s battery. Simply connect one end of the included dock connector–to–USB cable to the dock connector and the other end to the USB power adapter.
You can use the dock connector to synchronize. Connect one end of the same cable to the dock connector and the other end to a USB port on your Mac or PC.
Microphone: The microphone lets callers hear your voice when you’re not using a headset.
The iPhone 4 has two microphones. The one that appears on the top of the iPhone is used for FaceTime calls and also works with the main mic (located on the bottom) to suppress unwanted and distracting background sounds on phone calls by using dual-mic noise suppression technology.The top of the iPhone 4.